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Electrical System

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Automotive Electrics Basics - Part 1 - Terminology and Part 2 - Typical faults, symptoms, and diagnostic techniques

Ammeters_and_Voltmeters    Alternator/Dynamo    Anti_Run-on_Valve    Batteries_and_Chargers    Battery_Cut-off_Switch    Brake_Balance_and_Handbrake_Warning    Bulbs    Cable_and_Pipe_Routing    Clocks    Connectors_and_Terminals    Cooling_Fans    Cruise_Control    Fan_Belt    Fuel_Pumps    Fuses_and_Fusebox    Hazard_Flashers    Heated_Rear_Window    Heater_Fan    Horns    Ignition_Switch    Ignition_System    Ignition_Warning_Light    Indicators/Turn_Signals    Instruments    Lighter_Socket    Lighting    North_American_'Key_in'_Warning    Overdrive    Polarity    Radio    Relays    Schematics    Screen_Washers    Seat_Belt_Warning    Sealed_Wiring_Junctions    Starter    Steering_Lock    Switches_in_General    Tachometer    Wipers    Wire_Colours,_Terminal_Numbering    Wiring_Harness_Replacement    Won't_Start    Won't_Switch_Off!    Torque_Values    Links   

(Image posted by Geoff Hutton on the MGOC forum)

Indicator/turn signals and hazard flashers

  June 2018: Warning! It seems that new Lucas indicator flashers SFB115 8FL (for Mk2 cars and later) from some suppliers at least are in fact hazard flashers. Three from different suppliers so far, with two different batch numbers. The differences are subtle but have safety implications. The most obvious thing is then when operating the indicator switch nothing happens immediately as it should, the lights only come on after a delay. Another more important difference is that if a bulb should fail instead of the other bulb and the tell-tale lighting continuously and not flashing in order to warn the driver, the tell-tale (and the remaining bulb) will flash normally. A third difference is that instead of being able to flash two bulbs only (one shouldn't flash, three or more may flash very rapidly before burning out the unit), anything from one to four bulbs connected will flash at the same rate. These three differences are what denotes these flashers as hazards, and not indicators. I've written to Lucas/Elta and they were not aware of the problem, but were interested enough to ask for pictures of the markings on the item and packaging, and the Technical Manager said he would get some out of stock for testing. No feedback on that yet. Subsequently an NOS 8FL was purchased and that works as it should, and is usefully faster than the one that has been in Bee for 30 years, so I leave it in.

Indicator/turn signal schematics
Hazard warning schematics
Where is it?
Dash tell-tales
Fault diagnosis
Indicator Flasher Replacement May 2016
LED flashers
Adding hazards to earlier cars October 2010
A louder audible warning
The indicator/turn switch Added August 2008
And for the enthusiast (or the anal) the innards of each flasher unit

May 2019: A puzzling problem for Steve Henson-Webb on the MGOC forum. When using his indicators the dash tell-tales worked, but when using the hazards they didn't. The appropriate corners of the car flashed when they should. Unfortunately it wasn't clear that when using the indicators both tell-tales were flashing, nor was it mentioned that they were dimmer than usual. The problem was the earth wire to both tell-tales having become detached. That meant that when using the indicators the tell-tales were effectively in series to earth via the indicator bulbs on the side of the car that wasn't flashing, so both flash, albeit dimly. When the hazards are on both tell-tales have 12v on their 'live' sides, but no earths on the other, so neither flashed. The puzzling thing is that it was a 1974 CB, but on Mk2 tin-dash cars there is no earth wire for the indicator tell-tales that I'm aware of, the bulb holder picks that up from the bracket they are pushed in to, which is attached to the back of the dash. He says it happened after fitting a radio, maybe that interrupted the dash earthing somehow, but seems unlikely. Mk1 cars (which didn't have hazards from the factory of course) did use 2-wire indicator bulb-holders as the 12v supply was switched from the flasher unit and the earth supply came from the indicator switch. North American Mk2 with the padded dash, all V8s and all RB cars also have 2-wire indicator bulb-holders as they are mounted in plastic panels so need a wired earth.

The indicators are powered from one of two green (fused ignition) circuits - originally the one in the fusebox. But sometime in 1978 when the ignition relay circuit on RHD cars was modified to add a second in-line fuse between brown/white and green wires under the fusebox, the indicators (and tach, heater fan and GT GRW) were powered from one of these - the one with the thinner wires, the other with thick wires being for the cooling fan. For more information see the ignition schematics. On cars equipped with hazard flashers the green circuit goes via the hazard flasher switch to be connected when the hazards are off, and disconnected when they are on.

By all accounts indicators are the bane of an LBC-ers life. But like all things, they worked when it came out of the factory. If it doesn't work now then there must be a reason (or two or three), so it can be found and fixed.

But first - know the difference between indicator/turn flasher units (they are not relays, strictly speaking they are thermo-switches) and hazard flasher units:

  • With indicator flasher units as soon as you operate the switch the lamps should light up, and after a short pause they should start flashing off-on-off-on.
  • With hazard flasher units as soon as you operate the switch nothing happens for a short period, then they should start flashing on-off-on-off.
However that only applies to the 2-pin indicator flasher units used on Mk2 and later cars. Mk1 cars used a 3-pin cylindrical flasher unit that operates differently. It appears to be the same - i.e. when you operate the column stalk and look at the dash tell-tales they come on straight away, then after a pause they start flashing off-on-off-on. But if you look at the corners of the car you will see they are operating in anti-phase, i.e. when you first operate the stalk nothing happens, then after a pause they start flashing on-off-on-off, i.e. the same as hazards! This is because the tell-tale contact on the flasher unit shows 12v when switched off, and is why the column stalk needs two additional contacts to connect the appropriate tell-tale when the stalk is moved. This caused some confusion on a pal's TR3, which only has one dash tell-tale for both sides, which is wired direct to the flasher unit. This was glowing all the time the ignition was on, and operated in anti-phase to the corners of the car. He had been supplied an MGB flasher unit, whereas the correct Triumph flasher unit has the tell-tale contact normally off, so the tell-tale operates in synch with the corners of the car, and the indicator switch doesn't need any additional contacts. Incorrect supply for Triumph owners must be very common, as many suppliers quote the MGB item as being suitable for the TR2/3/4, but I did find the correct Triumph Lucas FL number (since mislaid) for my pal and he was able to get the correct item from the same supplier.

If you substitute an indicator flasher for a hazard flasher it will probably flash rapidly and burn out very quickly as they are only designed to flash two 21w bulbs (plus a 5w wing repeater on the 2-pin types). But if you substitute a hazard flasher for a 2-pin indicator flasher it will at first seem to work correctly, unless you notice the sequence (as above) is incorrect. This is a safety hazard, as it delays the lights coming on and hence the warning to road users. So many people these days seem to operate the indicators at the same time as they turn the wheel that the rest of us need all the warning we can get!

There are also 'universal' or 'heavy duty' flasher units that although they may have the correct sequence for indicators i.e. they come on as soon as you operate the switch, don't have the built-in 'bulb failure warning' of the originals. Really when fitting an alternative flasher unit you need to disconnect one corner and confirm that you still get this warning. On original MGB types this warning is that flashing stops altogether, and only one external bulb will be lit. On modern electronic units the remaining bulb should flash at double-speed.

To complicate matter even further there is another type of after-market indicator flasher unit intended for use with after-market LED bulbs, more on those here.

Originally the MGB used a cylindrical 3-pin flasher unit (GFU103, Lucas FL5), but this is not the same as modern electronic 3-pin flashers. On the originals the third pin is used to flash the dash repeaters via additional contacts in the indicator switch, whereas on electronic units the third pin is connected to earth. Mk2 MGBs used a rectangular 2-pin indicator flasher unit (SFB115 (was GFU107), Lucas 8FL) as the dash repeaters are now connected to the wiring going out to the corners of the car. Both the original MGB types are 'thermal' type flashers and the following information is from Steve Blakeway who was an employee of Lucas working on the 2-pin thermal flasher units and their electronic replacements for nearly 30 years: The moving contact is on a metal plate pressed from thin spring steel. The blanking and pressing of the spring steel gives it a 'set'. The thin strip was then welded diagonally such that the plate was deformed against the set. When the indicator switch is operated and passes bulb current through the thin strip it heats up and expands, which allows the plate to ping back to it's original set, opening the contact and extinguishing the bulbs. The current ceases and allows the thin strip to cool and contract. This pings the spring-steel plate back to it's previous position, closing the contact, illuminating the bulbs, and heating up the thin strip again, so repeating the process. It works rather like the Pop-o-Matic Dice Shaker in the game 'Frustration'.

As well as straight-forward disconnections causing non-working bulbs, the 2-pin MGB indicator/turn flasher is very particular about the amount of current it needs to work - it doesn't have to drop very far due to low battery voltage or bad connections before you start to get slow, or non-flashing where the lamps stay lit all the time. Incorrectly rated lamps will cause problems, as will 'tired' bulbs that were originally the correct rating but have become high-resistance internally with age. This is another difference to the Mk1 3-pin flasher units, which even with one bulb disconnected will try to operate and can give a faint click and a very brief flash of the other bulb. It's unfortunate that the change in design that meant they light the lamps immediately the switch is operated, also made them so sensitive to current. But on new cars out of the factory that wouldn't have been a problem, only to us 40 years down the road!

Hazard flashers, on the other hand, are designed to work irrespective of how many lamps are working. The car may have been in an accident and a corner may be smashed, but you want as many lamps as you have left to flash a warning to other road users, even if only one lamp is left working. Hazard flashers will also continue to flash even as the battery discharges and the voltage and hence current drops. Again, you want to warn other road users for as long as possible. Hazard flashers can be useful in de-bugging indicators. North American Mk2 cars had hazard flashers fitted from the factory. The circuit diagrams shows these as being cylindrical 3-pin with the third pin flashing an additional hazard tell-tale lamp even though the indicator/turn signal repeaters are also flashing. However the ATJ8880, Lucas 9FL flasher unit listed in the Parts Catalogue only has two pins, and from 1972 the circuit diagrams show the additional tell-tale being connected to the hazard switch instead, and a 2-pin hazard flasher unit is shown. V8s have the same part number listed which is shown as 2-pin in the diagram, and the same applies to UK cars when they got hazard flashers in 1974. UK cars never had the additional tell-tale. However there was a Lucas cylindrical 3-pin hazard flasher available at the time, similar to the original MGB indicator flasher, so perhaps that is where the confusion on the diagram stems from.

Some suppliers are showing SFB115, GFU2124 or GFU2125 as replacements for ATJ8880, but these are indicator flashers only capable of operating two 21w bulbs, they are not hazard units which need to flash four 21w bulbs. The correct item is SFB130, aka 35053.

Where is it?: April 2020

Indicator flasher units seem to be in much the same place for various years and markets, to the left of the wiper motor. Originally the hazard flasher and its fuse were behind the centre console. Eventually - probably 1977-on - the fuse moved to a more logical (and accessible) position below the fusebox, and the flasher unit to beside the indicator flasher.

Dash tell-tales: October 2019

Mk1 cars have two wires to the tell-tales as they have connections to both the flasher unit and the indicator switch and need insulated bulb holders 37H5181 similar to the ignition warning light. The bulb is an MES E10 screw-fitting (GLB987).

Mk2 CB RHD (and LHD without the padded dash) cars have a holder with only one wire to the tell-tale (13H1924), the holder picking up an earth from the bracket on the back of the dash panel. The same MES E10 bulb as above. In front of this bracket is a tube which concentrates the light onto a green plastic lens, which is positioned behind an arrow-shaped cut-out in the dash panel.

  Early padded dash have a unique dash fitting and a two-wire (green/white or green/red and black) claw-type bulb holder similar to Mk1 cars, and takes the same MES E10 bulb.

Later padded-dash, V8s and rubber bumper tin dash have a tubular lens pushed into the front of the dash panel, secured from the back with a spire clip. The bulb holder has two wires, the second providing an earth as the mounting panel is insulated, and pushes into the lens from the back. The bulb is a BA7S (GLB281) i.e. bayonet-type.

From 1977-on with the smaller squarer rocker switch the rear fog-light switch has an internal bulb (LES GLB921 screw fitting) for the tell-tale function showing orange as well as the night-time illumination showing green.

  Fault diagnosis: Indicators/turn signals

  Indicators/turn signals: Updated July 2015: From 1962-67 a cylindrical 3-terminal flasher unit was used, not be confused with later electronic 3-terminal units. After that a smaller 2-terminal rectangular unit was used, and the two differ as far as fault diagnosis is concerned. On the later type if a bulb fails or there is a disconnection in the wiring to it, then the indicator won't flash but the working bulb will glow continuously, making it easy to see which end you need to investigate. But on the early type this won't happen, except that you may get a very brief and faint flicker on the working bulb.

  Apart from that where indicators light but don't flash one side this printable schematic and chart should help you to plot the voltages through your circuits and locate any bad connections. You don't need the engine to be running but it is more realistic if it is from a voltage point of view, and won't flatten the battery (dynamo-equipped car may need a bit of fast idle to extinguish the ignition warning light). If you don't run the engine (saving fuel) then disconnect the coil to prevent it overheating which it almost certainly will do with the ignition left on for a long time (with the exception of some electronic ignition systems). Non-flashing could be due to a failed flasher unit of course as well as bad connections. An ammeter in place of the indicator flasher unit should ideally show 3.5 amps, if it shows 3.2 amps or higher but doesn't flash then the flasher unit is probably faulty. With bad connections a new flasher unit may well start them flashing again, but this can simply be due to its being new and more sensitive, as it 'burns in' they will probably slow and stop again. If you are investigating slow flashers, and they continue to flash slowly, it makes measurements easier if you bridge the two connections on the flasher unit to stop it flashing. See here for the results of the tests on Vee.

  This sensitivity to current was deliberate to give warning to the driver if a corner should have failed, otherwise traffic around you may not realise you are preparing to turn. Modern flashers use electronics (instead of a heated bi-metallic strip) and flash rapidly if one of the main lamps fails and are nowhere near as sensitive to slightly bad connections as the original 2-pin units. Some people fit a modern electronic flasher to their classic car when they get slow flashing from poor connections, not realising that they will still there and causing the lights to be dimmer than they should be. A pal fitted one of these a while ago, but on doing voltage tests for another issue more recently found he was getting less than 8v at each rear light. Whilst fitting an electronic flasher unit to get round 'slow flashing' problems because of bad connections may seem to have done the trick - temporarily, eventually you may have to find and fix the root cause(s), you might as well do it now and get brighter lights. Be aware that some aftermarket types flash at the same rate regardless of current and therefore give no warning of lamp failure, so if you wimp-out and fit an alternative flasher unit disconnect one of the bulbs with it fitted and make sure that the flashing speed changes. If not, you run the risk of being rammed up the back because the person behind had no idea you were going to turn so didn't expect you to slow down. Electronic flasher units have their own problems - or at least people have problems with electronic flashers, as I have known of at least two occasions where the driver was blissfully unaware that because one side flashed at twice the rate of the other it indicated bulb failure, they hadn't even noticed! As Einstein reputedly said "Only two things are infinite - the universe and human stupidity, and I'm not sure about the former." Likewise LED Bulbs have their own issues.

  As mentioned before the indicators circuit is: Battery - starter cable - brown circuit - ignition switch - white circuit - fuse (note 1) - green circuit - hazard flasher switch (note 2) - green circuit (note 3) - indicator flasher - light-green/brown circuit - indicator flasher switch - green/white (RH side) and green/red circuits (LH side) - indicator bulb holder - indicator bulb - indicator bulb holder - body earth (note 4) - battery earth cable. CB cars with twin-6v batteries also have the battery link cable.

Note 1: Later cars have an ignition relay and white/brown circuit between the white circuit and the No. 2 fuse.

Note 2: The indicator flasher is wired via the hazard switch so that it is disconnected when the hazard flashers are turned on, and only works when the hazards are turned off. This prevents the outputs from the hazard and indicator flashers from conflicting with each other, but more importantly prevents the hazards feeding power back through the indicator switch, indicator flasher, green circuit, fusebox and onto the white circuit and so energising the fuel pump and ignition (my thanks to Mark Childers for pointing this out). So don't be tempted to bypass the hazards switch if it is that which is causing your indicators problems.

Note 3: The 'green' circuit from the hazard flasher switch to the indicator flasher should really have its own tracer as it is no longer part of the 'real' green circuit.

Note 4: Rear light clusters on all cars and front indicator/parking light clusters on CB cars have the cluster picking up an earth from their physical fixings to the body. RB front indicators have a wired earth shared with the headlights/front parking lights.

Typical indicators faults can be "They don't work at all" or "They don't work on one side" or "They light but don't flash or flash too slowly" or "They flash but so do other lamps" or "They don't cancel".

  "They don't work at all"

Do you have hazards?

Yes - do they work?

Yes, but only some of them work - follow through the continuity of the lamps that don't work. Could be bad connectors, corroded lamp holders, blown lamp or bad earths. If only one side flashes with the hazards switched on it could be a dirty contact inside the switch or a bad connector in the green/white or green/red circuit as applicable. Then follow the following paragraph.

Yes, they all work - if all lamps are flashing then that indicates that there is continuity at the lamp ends of the green/white and green/red circuits, although they could still have connections bad enough to affect the rate of flashing of the indicators. Now check the green circuit for 12v through the hazard switch (which needs to be off. Note that dirty contacts in the hazard switch are a frequent cause of indicator problems that affect both sides) and the indicator flasher to the indicator switch (if you suspect the flasher unit itself just bridge its two contacts. The lights should light, but not flash). Then through either the green/white or green/red circuits out toward the lamps. Pay particular attention to any volt drops anywhere except across the indicator flasher itself, which typically drops about 0.25 volts when the lamps are lit (and 12v when they are in the 'off' part of the cycle).

No - see below.

No - check the green circuit for 12v through the indicator flasher to the indicator switch. Then through either the green/white or green/red circuits out toward the lamps. Pay particular attention to any volt drops anywhere except across the indicator flasher itself, which typically drops about 0.25 volts when the lamps are lit (and 12v when they are in the 'off' part of the cycle). If you suspect the flasher unit itself just bridge its two contacts. The lights should light, but not flash.

  "They don't work on one side"

If neither lamps on one side flash or light you could have one fault in the common circuitry e.g. the switch or the connectors by the steering column, or two (or more) unconnected faults in the wiring out towards the lamps. Track the 12v through the indicators switch and the green/white(RH side) or green/red (LH side) wiring out towards the lamps.

  "They light but don't flash or flash too slowly" Updated April 2013

This is an indication of either a failed flasher (which affects both sides equally) or bad connections out towards one or more lamps. Pay particular attention to the front indicator, although chrome bumper and rubber bumper are obviously different, both are subject to water and salt being thrown forwards by the wheels and hence corrosion. Chrome bumper cars earth through their physical fixings, and whilst rubber bumper units have a wired earth shared with the headlights it's connection to the light unit is external and unprotected, using a type of bullet. The bullet is large and hollow i.e. not crimped to the wire as elsewhere. The wire is stripped, pushed up the middle, and the conductors folded down the outside, then this is pushed into a flimsy clip. The result is poor - worse than the body earth arrangement of CB fronts and all rear light units. One of these on mine was losing nearly a volt, and the other nearly half a volt. Removed and cleaned up got then down to 0.2v and 0.1v respectively - a bit improvement but twice the rears. If the shared earth i.e. from the bullets by the headlights to the body earth is high resistance the indicators may not flash with the headlights on. If you replace the flasher unit with an ammeter ideally you will see about 3.5 amps drawn per side. The more this drops, the slower the flash rate will be, particularly with the engine stopped. But if you see 3.2 amps or above (i.e. satisfactory connections through the whole of the circuit) and it doesn't flash then almost certainly the flasher unit has failed. Note that replacing a slow flasher does have a good chance of speeding things up, but they usually have a 'burn in' period then slow a bit to their 'normal' flash rate, meaning you end up no better off. If you see 3 amps or less it might be an idea to go to the corners of the car and do the last few tests first, as it could be that you have incorrectly rated or very tired bulbs. As bulbs age the filament thins, which reduces the current, and that will slow the flasher. The symptom of this would be a good voltage at the light unit but still a low current at the flasher.

Investigating slow or non-flashing where the cause is low current is probably the most difficult electrical job on the car, and can be very frustrating, the only way to deal with it is in a logical and methodical manner. As well as being the most sensitive circuit on the car to bad connections, there are more connections in this circuit than any other - around 30 just to flash two bulbs on one side! Any electrical circuit will 'lose' some voltage in wiring and connections when carrying current (and ours have up to 50 years of oxidisation to contend with), so my recommended methodology involves taking voltage measurements at certain points along the circuit, all of which can be done with minimal disturbance to wiring and connections. By working along the circuit you can spot a sudden drop in voltage, which means there must be a problem between this point and the previous one. However rather than testing every single one in strict order, it's more efficient and will save time if you test certain key points first, then use that to decide whether the intermediate points need investigation or not. For example if you only see a 0.1v drop between two points that have three other connections between them, there is no point testing those three other connections. The first half of the tests are all on circuitry that is common to both sides, but after the indicator switch you needs to take one set of measurements for each side, and shortly after that one set for each corner. Whilst slow or non flashing both sides will lead you to think it must be a common problem, it's just as likely for there to be problems on both sides.

The ignition will be on with the engine stopped for these tests, so the coil should be disconnected to prevent that overheating. It also reduces the load on the battery. With 3 amps or more you will still be discharging the battery noticeably, and you will need to know when to stop or whether to connect a battery charger during the tests to avoid discharging it too much. The other thing is that while testing, and discharging the battery, its voltage will be dropping anyway, so you need to take this into account when you are testing along the circuit by periodically remeasuring the first test point, or you could be led to think there is more voltage being lost the further you go along the circuit than there actually is. If you only operate the indicator switch long enough to take each measurement, and turn it off while moving the meter from point to point, you will minimise the drain on the battery. Finally it's not going to be easy measuring voltage on either an analogue or most digital meters if the flasher is going, even slowly, so it makes sense to bridge the green and green/brown wires at the flasher unit so the lamps are glowing continuously while taking the measurements.

This schematic and list should help you plot the voltages through the circuit. The list works along the circuit connection by connection, but some are conditional i.e. only performed if a test earlier in time, but later in the circuit, shows a bad connection. You will probably end up with a progressively dropping voltage as you go from point to point. Writing these down you will see where the biggest drops are, and tackling those first will give you the biggest improvement. That way, when you get fed up, the worst ones should have been done! Note that the last few are earth tests so in an ideal world these will all be zero, so switch your meter to a lower range if appropriate. Any voltage seen in these tests indicates a bad earth. Note that as well as the centre contact of the bulb being a possible cause of a bad connection, which is inaccessible without removing the bulb, there is also a connection between the bulb base and the holder, the holder and the light unit, and the light unit and either the body (chrome bumper front lights and all rear lights) or the wired earth (rubber bumper front flashers), all of which can cause problems.

The attached shows the measurements on my V8, not because I had a problem but as a practical indication of the sort of figures you might get. The first thing to say is that I have a quality AVO analogue meter, and a cheap digital, and I got some weird and inconsistent results between the two. The first problem was that at the battery connections the analogue read 12.2v but the digital only 11.2v, both with everything switched off. I've seen this before with a digital dash voltmeter - which rather goes against the point of its existence. Subsequently I compared those two with a third, analogue Gunson's instrument, and with all three connected at the same time I got 0.5v difference between the original two, and the additional analogue instrument was lower again! It would be tempting to say the digital must be the most accurate, and the AVO reading high and the Gunson's low. But when doing earth tests at the first light unit (right front) with the digital it didn't matter whether the probes were connected or disconnected, the display kept hunting around the 200-300mV area. If I connected the probes together, or even put my thumbs on them, the reading stepped down to zero. So I tried my AVO and that immediately showed 0.9v on the bulb base, holder and light unit. So that, together with previously having found it increasingly more inaccurate as the resistance value got higher, means I don't have full confidence in it. Nevertheless, it is comparative values along the circuit that we are going to be looking for rather than absolutes, and as the digital is much smaller than the analogue I used the digital to move around the car and left the analogue connected to the battery so I could monitor it's reducing voltage through the test process. In the event I got half way through without seeing any drop (from 11.9v under indicator load) so stopped recording it for a while. I checked again near the end and it had dropped to 11.3v, after maybe 3 hours of switching the indicators on and off and moving from point to point.

  "They flash but so do other lamps"

This usually affects rear lamp clusters and front lamp holders of CB cars and is usually caused by a bad earth. Most noticed when another circuit in the cluster is powered at the same time as the indicators as other lamps flashing in time with the indicators, it is caused by current flowing backwards through any other lamps that share the same faulty earth to whatever other earth it can find. All rear lamp clusters, and CB front parking/indicator light units, earth via their physical fixings to the wings.

  "They don't cancel" Updated September 2007

A mechanical problem, this, rather than electrical. Up to the 77 model year cancelling is performed by a cam or peg at the top of the steering shaft engaging on one of two fingers projecting out from the switch. Early columns have a peg screwed into the shaft in a fixed position, later columns have a cam which is a tight sliding-fit on the shaft. With the indicator switch in the 'off' position the cam or peg clears the switch fingers as the wheel is turned in either direction. Operating the switch moves one or other of the fingers into the path of the cam or peg as the wheel is turned. When turning in to the corner the peg or cam passes under the finger, lifting it out of the way. Then when you straighten up the peg or cam pushes against the end of the finger to cancel the switch. From 1977 on the switch (both stalks on a single plate) fitted over the steering column instead of bolting to the side and includes a rotating 'cancellation' collar with two notches. The steering wheel itself engages with these notches to turn the collar and cancel the indicator stalk if it is operated. After-market wheels probably won't have the ability to engage with this collar, and so won't cancel, see here for suggestions on how to interface an after-market wheel to this type of switch. Cancellation is the same as before, i.e. on straightening up from a corner, but the mechanics of the operation are concealed inside the switch.

For both peg and cam types, with the wheel straight-ahead the peg or cam should be pointing at the middle of the indicator/turn switch. For the 77 and later type there is a rib on one side of the cancellation collar, and again this should be pointing at the middle of the switch. If the peg is in the wrong position on the shaft to cancel the switch correctly the column shaft, UJ and rack shaft have been incorrectly assembled. The UJ is clamped onto each shaft with a bolt, and this bolt passes through a cut-out in the shaft so that even if the bolt becomes loose the shaft cannot pull out of the UJ (the bolt has to be completely removed to withdraw either shaft from the UJ). However, although the column shaft only has a notch for the bolt, meaning that it can only be inserted into the joint in one position, the rack shaft has a groove machined all the way round so that it can be assembled in any position. Use this feature to get the peg in the correct position. You will probably then have to alter the position of the wheel on the column shaft (click here for how to remove the steering wheel) to get the correct 'straight-ahead' orientation of the wheel.

Problems can be caused by worn or broken fingers on the switch. Building up the height of the cam or judicious bending of the fingers with heat (don't break them!) can compensate for this. Broken fingers may be able to be jury-rigged - you will have to judge.

The sliding cam can become loose on the column and slip round instead of cancelling the switch. You could try removing the cam and closing it up a bit making it a tighter fit on the shaft, or degreasing and roughing-up both surfaces, gluing, or as a last resort drilling a hole and fitting a small screw through cam and shaft (but drilling holes in things like steering shafts isn't really recommended).

  Hazards fault diagnosis: The hazard warning circuit is: Battery - heavy current cable - brown circuit - in-line fuse - another brown circuit - hazard flasher - light-green/brown - hazard flasher switch - then out on the green/white (RH side) and green/red (LH side) circuits to the lamps at the corners of the car as with the indicators. The hazard flasher fuse was originally behind the centre console - inconvenient! - moving to under the fusebox, possibly around 1977.

Note: The indicator flasher is wired via the hazard switch so that it is disconnected when the hazard flashers are turned on, and only works when the hazards are turned off. This prevents the outputs from the hazard and indicator flashers from conflicting with each other, but more importantly prevents the hazards feeding power back through the indicator switch, indicator flasher, green circuit, fusebox and onto the white circuit and so energising the fuel pump and ignition (my thanks to Mark Childers for pointing this out).

These tests should be done with the ignition off, and all wiring connected, except where specified otherwise.

First check for 12v on the brown and light-green/brown terminals of the hazard flasher. Note: North American cars prior to 1972 have a third terminal on the hazard flasher with a light-green/purple wire. From 1972 on this wire was on the hazard switch. This is for the hazards tell-tale and should be ignored in all tests.

No 12v on either - check the in-line fuse.

12v on the brown but not the light-green/brown - hazard flasher faulty

12v on both - move on to the hazard switch

Hazard switch: Check for 12v on the light-green/brown. No 12v - break in the light-green/brown back towards the hazard flasher

12v present - operate the switch and check for 12v on the light-green/brown again

12v drops to zero - check the light-green/brown back at the hazard flasher again No voltage - hazard flasher faulty

12v still present at the light-green/brown at the flasher but not at the hazard switch - bad connection between these two points. Note late model cars have a multi-way plug and socket concealed behind the dash.

Light-green/brown at hazard switch still at 12v - turn off the hazard switch, turn on the ignition and operate the indicators to either side. Check for 12v on the green/white (RH side) or green/red (LH side) at the hazard switch No 12v on either green/white or green/red with the indicators flashing - break in the green/white and/or green/red between the flasher switch and the wiring between the indicator switch and the corners of the car. Note that on North American spec cars the green/red joins at a six-way bullet connector in the mass where the main and rear harnesses join together at the firewall by the fusebox, whereas the green/white joins on the back of the multi-plug for the indicator switch. After that, and on UK cars, both green/red and green/white join at the multi-plug.

12v flashing on and off with the indicators - hazard switch faulty. This can be confirmed by cancelling the indicators and turning the ignition off again, then bridging the light-green/brown to either the green/red or the green/white (or both together) wires that go to the hazard switch, removing the plug from the switch if required. If the remainder of the hazard circuit is good it will start to flash the lights.

Indicator Flasher Replacement May 2016:

I'd noticed Bee's flash rate was getting quite sedate, even driving along i.e. full voltage, and they wouldn't flash at all with the engine stopped apart from a brief click as you switched from one side to the other. I did my voltage tests and with one exception there was very slightly less voltage lost end-to-end than Vee, the one exception being in the 'new' indicator switch assembly which was slightly higher, but that only brought it back to the same as Vee overall. Two 21w bulbs directly on the output of the flasher unit were the same, the only thing that got them to flash - albeit slowly - (with the engine off remember) was when I added a 2.2W bulb to the 21W bulbs. So I reckoned the 1978-vintage flasher unit was probably getting tired, and ordered a new one. I was surprised to find that was twice the height of the old one even though it was the correct '2 x 21W + 5W'. Installed it does flash with the engine stopped albeit quite slowly of course, although I'm sure it's quieter. However I know these units are slightly more sensitive when new, which reduces after a short period of use to a 'long term' flash rate. After a weekend away it definitely is quieter, but more importantly noticeably slower then the old unit when the engine is running. The old unit gives 80 flashes per minute, the new one only 64, which is only just above the MOT minimum of 60 flashes per minute. Roger Parker said that in these days of frantic traffic one needs them flashing faster rather than slower, and recommended that the club shop send me another. They did, but that is even slower at 56 fpm and so below the legal minimum. I did some more tests with my three bulbs, and also powering the flasher unit off the purple circuit, which when combined eliminates almost all the cars wiring, on both the roadster and the V8. The upshot was that the fastest I could get a new flasher to run at was 76 fpm which is just about OK. The original unit connected the same way was flashing at 116 fpm, which is almost too fast, the legal maximum being 120 fpm. So the new units are definitely faulty, although they seem to be able to ignore connection and wiring resistances much better than the original units, much as the 3-pin electronic units do. Whereas the original unit showed a 60% increase in flashing rate between the two extremes of connection, the new units showed only a 15% and 20% increase. Neither do the new units exhibit the slight slowing when applying the brakes that the original units do. Whether this is just because they are new, or whether the bigger can means they are different inside I don't yet know. If only they flashed at a better rate when connected normally, they would be an improvement. I've sent the results of my tests to Roger, and await developments. In the meantime I opened up one of the new flasher units to find - not surprisingly - it is the same as another I have. I tried tweaking the contacts, which did make it flash at an acceptable rate at 12v, however with the engine running i.e. at 14v it's initially very erratic either galloping or not flashing at all before settling down to an acceptable rate, so on balance I have put the original unit back in.

July 2018:
Happened to come across an NOS indicator flasher in a red bubble pack for £5.50 on eBay so snapped it up. Ticks faster than either of the units that came with Bee and Vee, and on Bee flashes with the engine stopped, so far so good. However it's noticeably quieter, so a couple of times I've found I've left it on after a turn. September 2020: while testing other aspects of the lighting the indicators have gone back to not flashing with the engine off, just one tick changing from one side to the other as before, proving that there is a 'burn-in' period and they deteriorate slightly for the bulk of their life. Still plenty fast enough with the engine running.

Note that while modern 3-pin electronic flasher units don't suffer from the slow flashing problem, neither do they warn you of worsening electrical connections that will be resulting in dim bulbs.

  LED indicators Updated December 2017 Many new cars these days are being fitted with external LED lighting including indicators, so it is inevitable these are being offered by aftermarket suppliers as replacements for incandescent bulbs. The first thing to be aware of is that in the UK at least, and at the time of writing, external LED lighting is not legal for use on public roads, only off-road or at shows, and vendors for the UK market have to state 'off-road use only' somewhere in their advert. They are not specifically banned for cars before 1986, but there is enough conflict between two sets of regulations currently in force in the UK to make it a 'grey area'. Whilst the Police almost certainly won't stop you, and the MOT only checks for function (and adjustment of headlights), you should check with your insurance company first. I did, and was told they would not be acceptable, and they could affect any claim, even if I had informed them of the change (which you have to do). This law may surprise a child support lawyer in Columbus Ohio since similar lighting is legal in the US as long as the lights are covered or remain unlit on public roads. It is unlikely that a child support lawyer would be familiar with the specifics of all traffic laws.

Secondly they will not work correctly with either the original thermal or 'standard' electronic flashers - in the former case both bulbs will light but not flash, in the second case they will flash but very quickly indicating bulb failure. Some vendors supply a load resistor with LED lamps so that the original flasher units (thermal and electronic) flash at the correct rate, but then the 'bulb failure warning' feature in the original flashers will only detect resistor failure, not LED or wiring failure!

You can get indicator flasher units specifically for LED lamps which should flash them at the correct rate - 2-pin and 3-pin where the third pin goes to earth. But again, these do not tell you when a corner has failed and so are equally as unsafe as load resistors with standard flashers, and with some types if you connect more than one incandescent bulb to them you will burn them out. Also some contain a relay and make an audible click and some do not. April 2018: Out of interest I purchased a 3-pin type advertised as being for 0.02A to 20A so apparently suitable for anything from all-LED to all-incandescent, indicators and hazards. But on all-LED they just flashed once, even though there was a current of 0.9A. It needed an incandescent tell-tale bulb added to boost the current to about 1.3A before they would flash repeatedly. Ends

A supplier of a 2-pin type claims that they are the units fitted to BMWs (but at only £14 I find that unlikely). Also I'd be surprised if modern cars were allowed to get away with there being no indication of failure as IMO it is a significant safety hazard. On questioning the supplier they defended themselves by saying LED bulbs were much less prone to failure than incandescent which is correct, but there can still be wiring or connector failure as before which will have the same effect. They defended that by saying failure warning types were being developed but had no date for availability, something I find difficult to believe when they are supposed to be OE units. I've not been able to establish yet whether OE use does or doesn't have failure warning, but recently I was behind a Range Rover with these bulbs which stopped in the middle of the road prior to turning across the traffic without indicating. Cussing the driver under my breath I then noticed as he turned that the side marker was flashing at the correct rate! Which indicates (ho ho) that Land Rover at least may well be fitting these with no failure warning. In theory cars should detect disconnections in the wiring right up to the bulb holder as there is a load resistor inside the 'bulb', but that still won't detect failure of the light emitting elements, and they do fail, especially after-market components.

Note that if you fit LED lamps and the LED indicator flasher unit you will probably need to change the hazard flasher as well. Whilst hazard flashers are designed to flash anything from one to four 21w incandescent bulbs, they do still need a certain amount of current flowing through them, and the current from even four LEDs can be less than one incandescent (21 watts i.e. 1.75 amps). My 'standard' hazard flasher will - just about - flash a single 6w filament but it won't flash two 21W-equivalent LEDs.

About the only excuse for fitting LED indicators is they can be left operating for a lot longer in the event of a breakdown or accident without flattening the battery - unless you have installed load resistors at the same time and retained the original flasher unit!

  Adding hazards to earlier cars
Hazard flashers were standard in the North American market from the start of Mk2 production in late 1967, but not added to UK cars until the 1974 model year. Before adding hazard flashers to earlier cars it is vital to understand that the hazard switch must disconnect the standard indicators in some way, otherwise it is possible to have the fuel pump and ignition powered even with the ignition off and the key in your hand, which is obviously a serious safety hazard (pun not intended) especially in the event of a collision. If a hazard circuit is simply added to the indicator wiring then with the hazards turned on and flashing the lights, if the indicator switch should happen to be operated, power will feed backwards through the indicator switch, indicator flasher, onto the green circuit and through the fusebox onto the white circuit. Factory flashers power the indicator flasher unit through the hazard switch in the 'off' position, disconnected when the hazards are turned on, so blocking this reverse current path.

When adding hazards this reverse path must be disconnected in some way. Options are:

  • Obtain a later rocker switch and wire it exactly the same as the later switch. This will require cutting into the green circuit as well as connecting to the green/white and green/red lamp circuits, and the new hazard flasher. These switches are pricey, as well as not matching earlier toggle switches, but would be a good option for UK cars with rocker switches.
  • Use a generic on/off switch to connect the hazard flasher to the green/white and green/red circuits via diodes, and use a third (blocking) diode in the green circuit feeding the indicator flasher unit. Diodes can fail, disabling either hazards or indicators, or could cause both sides to flash with the indicators so burning out the indicator flasher.
  • Use a generic double-pole single throw switch with the hazard flasher connected to the two common terminals, the green/white to one of the normally open contacts and the green/red to the other, and a blocking diode in the green circuit feeding the indicator flasher.
  • Use a generic double-pole, double-throw switch, one half of the switch disconnecting the green circuit and the other half connecting the hazard flasher to the green/white and green/red circuits via diodes.
  • Use a generic double-pole double-throw switch with the green/white and green/red wires from the corners of the car connected to the two common terminals, the normally closed contacts connected to the green/white and green/red wires from the indicator switch, and the normally open terminals connected together and to the hazard flasher. Simplest in that it doesn't involve diodes, but does require cutting into both the green/white and green/red circuits instead of just the green circuit.
  • Hazard flasher modules are available as after-market add-ons, make absolutely sure these do disconnect or block the existing indicator circuit to prevent this reverse current flow. The vendors may have no idea what you are talking about, so always test after fitting by looking for 12v on the white or green wires at the fusebox with the ignition off, hazards on, and indicator switch operated to one side or the other. If the circuit is not blocking this reverse path you will see 12v switching on and off as the hazard flasher unit clicks, remove the unit, send it back (recorded delivery) explaining why you are returning it, and demand your money back.

There is also the hazard tell-tale to consider. According to the schematics UK cars don't seem to have had these (why would you need one when both the dashboard indicator tell-tales will be flashing anyway?), but North American spec always did. From 1972 this was fed by a light-green/purple wire off one of the contacts of the hazard switch and a 2-wire hazard flasher unit was used. In this case only the first option above can be used, as the tell-tale needs to be isolated from the hazard flasher unit and the indicator wiring when not in use, and only the factory switch (or similar hazard-specific switch) does this. The schematics show that from 1968 to 1971 a 3-wire hazard flasher unit was used, with the third wire feeding the tell-tale, and this type of flasher and tell-tale wiring can be used with any of the options above. 3-wire hazard flashers seem to have been used on a number of British cars of the era, still seemingly available from the likes of Rimmer, Canley Classics and others. Check they are capable of driving at least 4 21w bulbs, they may also be marked 'heavy duty'. Alternatively it may be possible to wire a tell-tale bulb in parallel with the 2-wire hazard flasher i.e. directly to its two terminals. This will flash the tell-tale in anti-phase to the corners of the car instead of in phase as with the factory and 3-terminal options, but should be legally acceptable for inspections.

Finally power to the hazard flasher must come from an always on, fused source. 'Always on' because the hazards need to be available with the ignition off and the key out, fused in case one of the corners of the car is damaged and the lamp holder or wiring is shorting out. Without a fuse this could cause a fire, adding to your woes. Factory cars were wired from the brown circuit via an in-line fuse solely for the hazard flasher, originally in the very inconvenient location of behind the centre console! Whilst it is technically feasible to power it from the purple circuit which is also always on and already fused, as this feeds the horns and other circuits accident damage may have shorted out that wiring elsewhere on the car and blown that fuse. This means that if you are going to the trouble of adding hazard flashers, a separate fuse off a brown wire is really the only sensible option.

  August 2013 After a pal had his TR6 written off by being rear-ended, just a couple of weeks after completing a two-year restoration to make things even worse, I decide I really need to fit hazards to Bee (Vee has them as standard). The TR6 didn't have them, although in that case I don't think it would have made any difference. The car had broken down on a dual-carriageway, was only half on the carriageway and half on a grass verge next to a crash-barrier, in clear visibility on a straight road just after a roundabout, with my pal back up the road warning people to keep over. Nevertheless this ... chap seemed totally oblivious of both my pal's warning as well as the car, almost hit him, then smacked right into the TR6's off-side rear corner which caused the perpetrator to spin and roll, coming to rest on its side. But anything that might improve visibility of these, by today's standards, small cars has to be of benefit and I decide to fit hazards before going any further with DRLs which a pal and I have been pondering for some time.

I didn't like the kits with the combined switch and flasher unit that you have to find somewhere to mount, and opted for the pukka rocker switch as I had a convenient blank on the centre console. Googling found the switch at Chic Doig Classic Sportscars Ltd, someone who I've been aware of in the MG world for a long time, at the reasonable price of £12.49. Ordered in the afternoon it arrives at breakfast time next morning - how quick is that? But I open it up to find it is a lighting switch instead of a hazard switch. Get on the computer to complain, to find an email from Chic to say that he realised he had sent the wrong thing, and had already sent the correct switch and to keep the lighting switch. I can't guarantee everyone will get a free lighting switch with each hazard switch, but again, how good a service is that?

More browsing for a hazard flasher leads me to Autopower UK Ltd, and I commit to buy at £8.79 before suddenly realising it is an indicator flasher i.e. only capable of flashing 2 x 21W, whereas you need a minimum of 4 x 21W, or 84W. Most these days are capable of flashing an additional pair of 5W side flashers and are marked '4 x 21W + 2 x 5W' or 94W in total. It's complicated by markings often showing '2/4 x 21W'. A hazard flasher should be capable of flashing anything from 1 to 4 lamps (plus side flashers), as one or more corners may have been damaged in an accident when you turn them on. Don't think that because it shows it will flash two bulbs, you can use it as an indicator flasher. Indicator flashers work differently in that they are designed to flash two and only two corners (plus side flashers), more than that will burn it out, less than that will not flash at the correct rate, which is a deliberate safety design feature to indicate (no pun intended) to the driver that one of the bulbs has failed. Also indicator flashers light the corners of the car as soon as the column stalk is operated, then after a short delay start flashing off-on-off-on. This is another safety design feature to give the earliest possible indication to other road users that you propose to change your lane or direction. By contrast hazard flashers do nothing when you first turn them on, and only after a short delay do they come on and start flashing. That delay in first coming on is unacceptable for indicator flashers. Any road up, as they say. I contact the supplier and they say that if I complete the transaction they will send me a hazard flasher instead, which duly arrives - again very good service.

As the hazard flasher unit has the same size and shape top as the indicator flasher I could have purchased clip BHA 4780 from several of the usual suspects and screwed it to the bulkhead beside the indicator flasher. However I opted to cable-tie it to the cross-brace by the steering column instead. So for just over £20 I have the makings. eBay kits are more than £40, and some aftermarket kits don't isolate the indicator circuit when the hazards are on which can be dangerous as described above.

The switch has round pins for a multi-way plug rather than spades, but I have an old harness from the rewire of a 1980 many years ago that will have had hazards, so can cut out that plug and the appropriate length of wiring to fit Bee. However I search the harness and can't find it, and subsequently realise I had already cut out the plug for a pal who was fitting hazards to his roadster! Never mind, late harnesses had a separate dash harness with three multi-way plugs and sockets connecting it with the main harness. The switch has four pins in one block (the 'hazard' connections), and another two spaced further away (the indicator flasher connections). The spacing in the harness sockets is such that it will fit the block of four, or the block of two, but not all six. So I cut the socket up into a block of four and a block of two!

It should be possible to remove the pins from the wiring side of the socket but it needs a tube of a precise internal diameter to fit over the business end to compress two little tangs, and thin-walled enough to fit between the pin and the tube in the socket. I spend a little time swaging down and drilling out a length of aluminium tube to make such a tool, without success. But then as I'm going to cut the wires off the pins and attach new wires of the correct colours, I simply push the pins all the way through the socket body from the wiring side. Although the block of four and the block of two seemed to be making a firm connection to the pins I test-fitted each pin once removed from the block. It's a good job I did as the switch pins are a smaller diameter than those in the 'male' half of the multi-way connector, so I pinch up the females to make a more certain connection.

I want to solder the wires to these pins, which have been spot-welded then crimped round the insulation. I use a very small drill through the cut end of the wire to remove it and open the outer insulation crimp up a bit, then use pliers to open it up fully and remove the strands of copper and remainder of the insulation. Five wires of the appropriate length to reach from the hazard switch to the column switch connector and indicator flasher, which are conveniently close together, are cut from the old harness in the correct colours: Two lengths of green for the indicator flasher, green/white and green/red for the flashers, and light-green/brown for the connection to the hazard flasher. Soldered to original inner conductor crimp, and closing the outer crimp around the insulation makes a neat connection.

After all that I subsequently found this!

The pins are then pushed into the socket bodies from the wiring side - light-green/brown, green/white and green/red to three of the block of the four, and the two green wires to the bock of two. The three wires can go on any of the four pins as with the hazard switch off each of these pins is isolated from everything else, and with the switch on they are all joined together (but nothing else). The fourth, unused pin would be for an additional tell-tale, but UK cars didn't seem to have this, and you already have the two tell-tales on the dash in front of you anyway. Again the two green wires can go on either of the two pins as with the switch off they are connected together (and nothing else) and with the switch off they are isolated from everything, i.e. the opposite to the block of four.

The other ends of the five wires need suitable connectors. The light-green/brown to the hazard flasher is simple - that just needs a female spade. The green/red and green/white will have to tap into those coloured wires on the harness side of the column switch multi-plug. I have had problems with Scotchlok connectors in the past, although that does seem to have been with wires that are thinner than the factory standard gauge. I've already used a pair to tap into those wires for the alarm I fitted many years ago. For some reason that alarm only had one wire to flash the flashers, but they have to be isolated in normal use or the indicators won't work! I had used a three-way 'chocolate block' connector to connect the single wire from the alarm, via two diodes to the two indicator wires, so simply added my two wires from the hazard switch to that chocolate block. I don't like cutting wires so for the greens I put a male spade on one, that goes into the factory green female that is removed from the indicator flasher, and a female spade on the other to go back on the indicator flasher. Note that if you have used the 'spare' spade on the indicator flasher as a convenient source of fused ignition power for an accessory, that will have to remain with the factory green somehow, or it won't work with the hazards on, which may not be a problem anyway. That leaves a permanent, 12v, fused supply required for the hazard flasher. I had a 35 amp inline fuseholder - again from the old harness - that already had brown wires both sides, so it was just a matter of attaching a female spade to one, and joining the other to the brown wire on the harness side of the multi-plug for the ignition switch with a Scotchlok. Again this should be reliable as they are both heavier gauge wires.

Power back on, flip the hazard switch, and it ticks merrily away with both tell-tales flashing. Switch that off and turn the ignition on and check both right and left indicators to make sure I hadn't disturbed anything there along the way. All is well so I wrap the five wires with harness tape (non-sticky) for neatness, although you can only see a couple of inches or so and even then by grovelling under the steering wheel.

  A louder audible warning

Never the loudest ticking, particularly at higher speeds in either roadster or GT, and some without the hearing sensitivity of a bat might find themselves inadvertently leaving the indicators on when they shouldn't be, you can add a buzzer to give more of an audible warning. Get a 12v dc buzzer and simply connect its two wires to the two terminals on the indicator flasher. Some electronic 'buzzers' are polarity conscious and will have red and black wires in this case, and for negative earth cars connect the red wire from the buzzer to the green on the indicator flasher and the black to the light-green/brown wire. For the earlier positive earth cars connect the buzzer the other way round. This will probably work on 'modern' cars too.

When you first operate the indicators you won't hear anything - don't panic! It is only when the lights go out on the first click of the flasher that the buzzer will sound, i.e. it operates in anti-phase to the lights. If you find the buzzer too loud you can always wrap a couple of turns of insulating tape or similar round it. However the cheap electronic buzzers make a pretty horrible sound, and even the piezo type can get annoying, so I'm experimenting with something to make a louder clicking noise with my NOS original which although flashing quicker is quieter than the old one ... watch this space!

February 2020: An enquiry on the MGOC forum reminded me that I hadn't updated this. My first thought was to wire a small loudspeaker in series with a capacitor. The theory being that although the impedance of a typical speaker is far too low to wire across the flasher unit and would affect both it and the lamps, adding a capacitor would prevent that but allow to capacitor to 'charge up' and discharge via the speaker each time the flasher contact opened and closed. I used to have a couple of speakers from small transistor radios I messed with decades ago, but couldn't find them. Got one off eBay but it was much smaller than expected and was way too quiet.

Next thought was a solenoid where the ends of the plunger were exposed, and positioned in a box or by a bulkhead the plunger would hit the sides of the box or the bulkhead so making a noise each time it operated and released (in a box) or just on the one stroke (bulkhead). Ordered one of those, but in the meantime I discovered an old GPO electronic sounder with three volume settings. Tried that and like Goldilocks and the three bears one setting was too loud, another wasn't loud enough, but the third setting was just right. It's also quite a melodic sound very different to the harsh 12v buzzer, so that's as far as I went.

The MGOC forum reminded me that I had also seen buzzers for motorcycles, including one type with a delayed response of 20 flashes or so before it started buzzing. Some of these have an additional feature that if you sit there with your brake lights on the buzzer is muted until you release them. As Dave Birkby said - "bizarre". Whilst I can understand car drivers sitting at traffic lights with a foot on the brake (instead of selecting neutral and applying the handbrake ...), do bikers habitually do that? Even though modern bikes light the brake lights from both front and rear brakes? And one motorbike forum was discussing a system where the buzzer only sounded once every ten or do flashes. Both relatively easy using a chain of bistables or JK flip-flops, should you be so inclined - four to give you a count of 8, five for 16.

  Indicator/Turn Switch Updated December 2009

Cowl Positioning

No less than 13 variations over the years, although several were to cater for LHD and RHD of course, plus other territorial variations.
  1. Cars to chassis number 161086 had a switch with contacts for selecting which dash tell-tale would be lit as well as contacts for controlling which side of the car would be lit. There were three variations on that - the second being to angle the stalk closer to the steering wheel, the third had what Clausager describes as "longer peg for more positive location". Only one replacement switch seems to be available - BHA4628
  2. From chassis number 161087 non-North American cars up to chassis number 187169 (roadster) and 187840 (GT) had a switch with a headlamp flasher - BHA4898, except Japan which had a switch without the headlamp flasher - BHA4897.
  3. North American Mk2 cars and non-North American cars from chassis number 187170 (1969 model year) up to chassis number 219000 (1970 model year) had a switch with dip/main, headlamp flasher and horn functions - BHA4948
  4. From chassis number 219001 (1971 model year) until 410001 (1977 model year) all markets had the horn button back on the steering wheel, 37H8050 for chrome bumper, 37H8101 for RHD rubber bumper and all V8 with legends for function, 37H8523 for LHD with words for functions.
  5. For the 1977 model year for the remainder of production the horn button returned to the indicator stalk, AAU4991 for RHD, AAU4995 for USA, AAU4993 for Canada. These act as the mounting plate for wiper switch (AAU4992, AAU4996, AAU4994).
Cancelling: For cancelling, cars up to chassis number 187211 (basically 1970 models that began at chassis number 187170 in September/October 1969) had a peg screwed into the column. After that cars have a clip which is a tight fit on the column but can be slid round it. Both should be facing the switch with the wheel straight ahead (May 2019: Three people on the MGOC MGB forum state their peg faces away from the switch, and the wheel needs to be turned 3/4 before it will cancel the indicators - OK for a T-junction, but nothing else. I've asked what others with a 1969 or earlier are like i.e. are any 1/4-turn as for the later system). The inconvenience with the early peg is that the whole column has to be turned in the UJ to get the correct alignment, and then the wheel turned on the column, whereas the clip can just be slid round to the correct position. Both types slide under fingers on the switch and lift them out of the way as you make the turn. With the early type as the wheel is returned the peg catches the metal finger, which lifts up the spring that is holding the stalk to one side, and the stalk should return. June 2015: Note that this type of column inner slides freely in the tube and if removing and refitting or replacing the column as a whole you may have to adjust the position of the outer in its clamp brackets, i.e. slide it up or down relative to the inner, to get the indicator switch in the correct position relative to the cancelling peg, even though the switch position on the tube can be adjusted to some extent. The position of the inner is determined by the U-joint and rack.

On the later type of indicator switch with plastic fingers the cancelling cam engages with the end of the finger and physically pushes the switch back to the central position. The fingers can wear such that the cancelling cam just lifts the fingers up again rather than bearing on them to cancel the switch, as well as the fingers having broken off or the cam being in the wrong place or missing.

Note that the clip-type cancelling cam or striker changed twice - once in June 73 on 4-cylinder cars from BHH254 to BHH1301, and again in September 74 for rubber bumpers to BHH402. This later change was for the full energy-absorbing column and column-stalk mounted OD switch that V8s had always had, but neither column nor switch seem to have changed on 4-cylinder cars in June 73. Roadwarrior says one was taller than the other, but he also says that when that is fitted to the wrong car the problem is that it causes the indicators to cancel as you start making the turn as well as when you straighten up again. But that is a different problem to the one that led up to him making that comment on the MG Enthusiasts Forum - non-cancelling - and may be the same cause but in the other direction i.e. the lower cam fitted where there should be the taller one. I've had to build-up the one on Bee, possibly after I changed the switch but I can't be sure. The V8 with the original switch (not changed by me at any rate) and striker has never been a problem.

  February 2020:
I get both cowls off and compare the cams and columns. The upshot is that the V8/RB cam is 'taller', but as well as that the column shaft is wider. So whilst in error the CB cam could perhaps be forced onto the V8/RB shaft it may well not be tall enough to push the indicator switch fingers back. Also whilst the V8/RB cam being taller may operate the CB indicator switch better, it will be a looser fit on the smaller column so may not stay in place. Possibly 'pinch it up' enough to grip, but the curvatures would still be different.

  Update September 2007:

1977 (and later) model-year cars have a special wheel boss which engages with a cancellation collar on the indicator/turn switch. In some ways this 77-on arrangement is best because all that needs to be done is to correctly align the steering wheel for the straight-ahead position. But if an after-market wheel is fitted, or if the later dual-stalk column switch is fitted to an earlier column, the wheel won't have the necessary protrusions to engage with the slots in the cancelling collar. The later clip could possibly be fitted to the column shaft, but is too wide to fit in one of the slots in the cancelling collar. A peg screwed into the column shaft would work, but I would draw the line at drilling a hole for it. On a friends car with a non-standard wheel I made a part out of a bit of scrap metal which joined together two handy holes in the back of the wheel boss, to the two slots in the switch cancelling collar.

Shortly before getting my hands on this 1980 UK model Barrie Robinson was seeking advice on cancelling indicator/turn switches on his car, which is a bit of a mish-mash of years, and he wasn't sure which column he had. He had bought a new 77 and later switch as the old one broke, but having a Moto-Lita wheel was left with this problem and didn't really want to splash-out for a new switch. I sent photos of what I had done to him, which gave him the ideas as to what to do with his wheel, making a neater job of it than I did.

June 2018:

Another possibility where there is an existing through-hole in the boss, is to use a rod or bar in the hole to engage with one of the slots in the indicator switch. Pre-1977 and after-market wheels may have a suitable hole, originally used for the centre horn-push pencil or connection wire, once the slip-ring for the horn connection is removed.


Lighter Socket November 2018


Going by the Leyland Workshop Manual schematics it was optional in all markets until the 1973 model year when it became standard, although Clausager says it was standard on North American Mk2. It was always illuminated with the parking lights, under the control of the panel light dimmer rheostat/switch.

When dealer-fitted it was powered from the white circuit on the ignition switch on Mk1 cars, i.e. unfused and only available with the ignition on. On the first year of RHD and non-North American LHD Mk2 models it was powered from the brown circuit at the ignition switch i.e. now available at any time but still unfused. 1969 and 70 RHD and non-North American LHD models were powered from the accessories position of the ignition switch but still unfused. 1971 RHD and non-North American LHD models were powered from the accessories position of the ignition switch, but were now fused from the 'accessories' fuse that powered the wipers and heater fan. All Mk2 North American spec cars, and from 1972 onwards all other models, were powered from the purple circuit i.e. fused and always available. When dealer-fitted it may or may not have needed a dedicated earth wire, but when mounted in the various plastic centre consoles it will.

There are many different types - some where the whole of the removable part is pushed into the socket against spring pressure and locks in position to heat it up, then pops out when hot. Others with a smaller 'push-button' inside the removable part that is pushed in and pops out. When pushing in to start heating the centre connection which is a circular disc gets pushed into a spring clip that retains it. This clip is bi-metallic so as the element heats up so does the clip, which starts opening up, and eventually releases the disc to pop out. Typically they are retained in the bracket or console by a large sleeve that screws onto the lighter from the back. This may have a large slot on one side for the bulb holder to clip in to, by pinching the sides of the holder.


22nd March 2021: MOT rules changed again to allow LED and HID conversions on cars first registered before 1st April 1986!

1st January 2021: MOT rules have been changed to fail cars with LED headlamp conversions:

4. Lamps, reflectors and electrical equipment
4.1. Headlamps
4.1.4. Compliance with requirements
"Existing halogen headlamp units should not be converted to be used with high intensity discharge (HID) or light emitting diode (LED) bulbs. If such a conversion has been done, you must fail the headlamp."
The irony is the phrase 'Existing halogen headlamp units'. Most MGBs came out of the factory with non-halogen headlamps, so even this has created another 'grey area', they probably should have used the term 'incandescent' instead.

October 2020: The legality or otherwise of LED external lighting, from Classic Car LEDs and the Federation of British Vehicle Clubs.

Parking Lights
Switch Connections
'Lights on' Warning Buzzer
Number Plate Lights
Brake Lights
Indicators/Turn Signals
Instrument Lighting
Ignition Warning Light
Map/Interior Lights
Roadster boot/GT loadspace lights
Reversing Lights
Hazard Flashers
Side-marker Lights (North America)
Fog & Spot lights
Switch Illumination
Daytime Running Lights (DRLs)

Chrome bumper front and all and rear park/brake/indicator light clusters rely on the physical fixings to the wings to pick up an earth, as do number-plate lights that are mounted on the bumpers and overriders. Corrosion, particularly at the front where both front and rear of the panel are exposed to water and salt, can cause problems with these lights, rear clusters being inside the boot/load space are protected to a large extent. When there is a bad earth feeding a light unit with more than one bulb or filament such as chrome bumper front park/indicator light units and all rear light units you will get interactions between them when more than one is powered, i.e. some being dimmer than they should be and others glowing dimly when they shouldn't, known as 'discoing'. Rubber bumper front indicators have a wired earth, shared with the headlights, as do the front 'parking' lights which are part of the headlamp assembly, and these can also experience unwanted interactions if the fault is in the earth wiring or its connection to the body. Reversing lights and number-plate lights that are attached to the number-plate backing-plate also have a wired earth.

  With any bulb you can get a bad connection between the bulb base and the bulb holder causing dimness, with dual-filament bulbs it can cause unwanted interactions between brake lights and parking lights as well, but the single filament bulb for indicators (usually) will be unaffected. If multiple circuits on both sides are affected particularly when the indicators are being used i.e. 'discoing' then the problem is more likely to be where the light unit is attached to the wing. Special 'nuts' (BHA 4242 'Dotloc', NLA, use 10/32" UNF with star-washer) were used with a spike that scratches through the paint to get a connection - pretty crude but there we are, and being in the boot/load space it's better protected from wet and salt weather than other light units. I've also heard of a problem causing interactions between dual filament stop and parking light circuits where the connection between the bulb-holder and bulb was good, but the bulb holder was making a poor connection to the base of the light-unit. You can test for this from the back i.e. inside the boot or luggage space. March 2020: This has just cropped up again on the MGOC forum where the owner noticed the parking lights had started coming on every time he applied the brakes, but there were no interactions involving the indicators. Cleaning everything in sight seems to have fixed it, but no root cause tested for or identified. Incidentally he first noticed this when all-LED lighting was installed, still there when standard bulbs were installed. Now the standard bulbs work as they should, but LED stop/tails cause the original problem again.

One oddity on early cars (for those used to later ones) is that the main harness only has one group of bullets at the front, not one by each headlight as on later cars. This reaches to the middle of the car i.e. behind the latch, and the tails from both headlights and parking/indicator lights also reach the middle of the car. At least, they did originally, but it seems some current stock has tails that only reach the later main harness bullets by the headlights. These tails are not itemised in the Parts Catalogue, suppliers have them as BAU2110 (for CB cars, BAU2111 for RB)

Later harnesses have a group of bullets by each headlight, which should be relatively easy to access on cars other than V8s and 4-cylinder 1977 model year and later from between the radiator and the slam panel. On the others you have to remove the mesh grille, and access is still pretty restricted.

  Parking lights until 1970: (aka side- or position marker, but not to be confused with North American 'side-marker' lights!)

The parking lights were not fused originally. Mark II cars introduced fuses, although for 1968 and 1969 the fronts were on one fuse and the rears on another, so if you had a fuse fail you lost both at one end, a particular problem at the rear as you lose all lighting until you brake. The fuses were of the in-line type, installed where the rear harness joined the main harness near the fusebox. Fuses can be added to Mk1 cars quite easily to make them the same as 68/69 cars.

Did you know ... that the front indicator/side-light (position marker) assembly moved closer to the grille in 1969 to meet a new European requirement that the position marker light be vertically below the centre of the headlight? See the end of this article on History of the Australian assembled MGB By Tom Aczel.

June 2020:
At the same time the location of the studs on the front indicator/side-light unit seem to have moved from being in-line to being off-set. The original in-line arrangement may have been so the light units could be fitted either way round i.e. indicators to the outside instead of parking lights, as Clausager says some export markets may have required. But it's more than likely that some were fitted that way round when they shouldn't have been, which is perhaps why the studs were moved so the light units can only be fitted one way round. The Leyland Parts Catalogue and suppliers such as Moss Europe and Brown & Gammons only list one light unit (BHA4966), and with suppliers showing both types of wing (with Moss showing the two different stud arrangements) it begs the question of how can the one light unit fit both wings? This question arose when Dave O'Neil wondered why, when he needed to replace one on his Mk1, neither of the NOS units he had in stock had studs in the right place for his wing, in fact one didn't have any studs at all! In the end he decided not to drill the wing (as someone suggested), but to drill holes in the correct places on the unit he had with no studs. He went to the extent of squaring them off, and used the studs from his old light unit, they pressed out and back in quite easily (as I found with a number-plate light unit). The wing aperture is also different but that doesn't seem to hinder fitting modified later units to the earlier wing.

This reminds me of an issue I had fitting new ones to the roadster - the chrome surround was pressed up against the paint when everything was screwed together, and I'd seen that had cut into the paint on a concourse example at the Classic Car Show. I ran a nut onto each stud first and that spaced it away, but left visible gap through as the sponge pads are not thick or dense enough. But a couple (from memory) of extra pads each side solved that.

Parking lights 70-on:

For the 1970 model year a four-fuse fusebox was provided, the additional two fuses (at the top) separately fusing each side, with additional wires run to the front and the rear of the car. This was a much better arrangement which in the event of a short and a fuse blowing you still had one front, one rear, and the number plate light on one side still working. There is only one wire (red/green) feeding the front of the parking light fuses - they are linked there, which means if refitting these fuseboxes you must be careful to fit it the right way up, or you can get the brown and purple circuits linked to the green and white circuits, i.e. effectively powering the ignition all the time. If one side has failed check the cleanliness of the fuses, fuse holders and connections. Be aware that the fuse holder is riveted to the connection spades on the back of the fuse block and corrosion can also occur here.

From 1970 North America used a dual filament 21w/6w bulb for the front indicators and parking lights for both CB and RB models, with an all-amber lens. Prior to that it seems that the lens used with the two separate bulbs could be either mixed amber and white as per non-North American models, or all white.

Parking lights, rubber bumpers:

North American spec cars got the same one-piece amber lens in the front bumper as RHD and other LHD cars, but the light-unit is different as it contains a dual filament 21W/6W bulb with offset location pins, the same as the stop/tail lights. This means that when the lights are on the indicators flash bright-dim-bright-dim instead of on-off-on-off. The Leyland diagrams are confusing as they still show the same two-bulb light unit as for chrome bumper cars, instead of a single bulb with two filaments as are shown for the stop/tail lamps. As the Advance Autowire diagrams show all lighting filaments separately there is no indication as to which is shared with which, for light units or bulbs.


LED park/stop/tail lights
Many new cars these days are being fitted with external LED lighting including stop/tail lights, so it is inevitable these are being offered by aftermarket suppliers as replacements for incandescent bulbs. The first thing to be aware of is that in the UK at least, and at the time of writing, external LED lighting is not legal for use on public roads, only off-road or at shows, and vendors for the UK market have to state 'off-road use only' somewhere in their advert. They are not specifically banned for cars before 1986, but there is enough conflict between two sets of regulations currently in force in the UK to make it a 'grey area'. Whilst the Police almost certainly won't stop you, and the MOT only checks for function (and adjustment of headlights), you should check with your insurance company first. I did, and was told they would not be acceptable, and they could affect any claim, even if I had informed them of the change (which you have to do). Information on legality or otherwise from Classic Car LEDs and the Federation of British Historic Vehicle Clubs.


Main-beam Tell-tale
Headlamp Flasher
Trim Ring
Headlamp Adjustment
Headlamp Mounting

As far as I can tell up to the 77 model year MGB headlamps were sealed beam. In the UK prior to 1970 GLU101 60/45W, then it gets a bit confused. The Parts Catalogue says for GLU101 'use before BHA4999' but that number isn't listed in the catalogue index nor does Google show anything for it. The next entry for 1970 to the end of chrome bumpers for 4-cylinder and V8 says GLU106, which the V8 Driver's Handbook (only CB cars) says is 75/55W, but the late CB 4-cylinder Driver's Handbook says 'GLU101 75/55W'. For rubber bumpers GLU123 is listed, and again I can only find two references both saying it is a sealed beam 75/50W with pilot light. For 1977 on H4 GLB472 halogen bulbs were used which any number of sites say is 60/55W. There were many variations for other markets and years. Brighter halogen bulbs are a direct replacement in these 77 and later cars, but to fit them to earlier cars you also need an H4 conversion. Many variations of these, some are described as having 'flat' glass, Vee has H4 with a domed glass (presumably a PO mod), although the dome is only half the height of that on Bee's sealed beams. They both have various ribs and patterns moulded into the glass so you have to see them side by side or measure the protrusion of the dome to see the difference. The truly flat moulded glass variants are a little more obvious. But there are also variants with plain flat glass where all the focusing and beam shaping is done in the reflector rather than having a plain reflector with the moulded glass as originally, and these look very different.

There have been comments about how poor sealed-beam headlights are and at one point they were uprated slightly for the UK market. When converted to H4 halogen the wattage reverted to the earlier value, however it's quite likely that the perceived brightness did increase which can be done through manufacturing techniques while keeping the nominal wattage i.e. current drawn the same (see Uprated Halogen). However the difference between sealed beam and H4 on the MGB is negligible compared to the difference between H4 and HID on modern cars.


The headlamp always used a 3-pin connector. On sealed beam rubber bumper cars it was combined with a holder and shroud for the pilot light to hold the pilot light against a 'window' on the sealed beam unit. From 77 on the halogen connector supports a gaiter that carries a separate bulb holder and positions the pilot bulb in a hole in the reflector assembly.

Headlights were never fused from the factory and if uprating them with higher power halogen and particularly with relays consideration should be given to fusing them.

Headlights have a wired earth, to a bolt near the right-hand headlight on early cars, moved to near the fusebox on later cars, probably with the alternator in 1968, but definitely with the starter relay in 1970.

On these later cars the main harness has several bullets and a tail by the right hand headlight for lighting and horn that side. The three headlamp wires are duplicated as one set brings power in to that point, and the second set feeds power back in to the main harness which then goes across to the left-hand side. Additionally there are single wires each side for the parking and indicator lights, and a 2-wire (until 1977, then a single wire) tail each side for the horns. One disadvantage of this arrangement is that the main and dipped beams for the left-hand side have to go via double bullets by the right-hand headlight as well as single bullets by the left-hand headlight, giving more opportunities for poor connections than the earlier arrangement, and these bullets suffer most from corrosion due to their exposure to the elements.


There was a floor-mounted dip-switch until the 1970 model year, column-mounted after that.

The column mounted dip-switch can be a bit difficult to puzzle out as it incorporates a headlamp flasher, indicator/turn signal, and on some years the horn wiring as well. The accompanying pictures show which contacts are which as far as the dip/main/flash circuits go. Several problems can develop with this unit, like failure to flash or light the appropriate lights, failure to cancel, loss of spring tension, etc. There is some scope for repair, although like many components of that and later eras they were only intended for one-off assembly and use, replacement thereafter, which isn't cheap.

As far as the wires go:

  • Blue is the headlight feed into the dip/main part of the switch.
  • Blue/white goes out to the main beams.
  • Blue/red goes out to the dipped beams.
  • Purple is the feed for the main beam flasher (goes out on the blue/white).
  • Light-green/brown is the feed in from the indicator/turn signal flasher.
  • Green/white is the feed out to the right-side indicator/turn signal bulbs.
  • Green/red is the feed out to the left-side indicator/turn signal bulbs.
  • Purple/black is the feed out to the horns.
  • The dip-switch should have three fore and aft (towards you and away) positions: Clicked towards you lights the dipped beams. Clicked away from you lights the main beams. Both of these are only when the main lighting switch is in its 'headlights on' position. In the dipped beam position the lever can also be pulled towards you against spring pressure to light the main beams in 'flash' mode, and this is independently of whether the main lighting switch is on or off. When released the lever should return to the central/dipped beam position to extinguish the main beams. If the lever is pulled towards you when the headlights are on, the main beams will be illuminated from the headlamp flasher circuit as well as the dipped beams from the main lighting circuit.

    Some of the contacts are fixed and others are 'springy'. The springiness applies pressure to the contacts to give a good electrical contact, but all the contacts can burn and blacken over time which can reduce headlight brightness and cause the switch to get warm in use. Cleaning of all the contacts and careful bending of the spring contacts can restore functionality, but it is easy to overdo it and mess things up even further. The contact springs are nothing to do with limiting the fore and aft movement of the stalk or the spring return from the flash position, they are derived from plastic 'springs' on the switch body and arm, as indicated in the accompanying pictures.

    Main-beam Tell-tale:

    Fitted in the speedometer on Chrome bumper cars except V8, in the panel by the speedometer on V8s and RB cars. In the former case it uses a 'claw' type single-wire instrument bulb holder 13H1924 picking up an earth from the metal case of whatever it is pushed into. In the latter case it uses a 2-wire bulb holder and a wired earth (BCA4780) as it is fitted to a plastic panel. I suggest the original reason for fitting them was with the push-push dip switch as that gives no feedback as to which way it is switched. Our column stalks will tell you at a touch, but modern pull-pull stalks take us back to 'no feedback' and are an abomination, I have to look at the tell-tale on my ZS 180 to see if they are on or not when first turning on headlights. It would be better if they didn't 'latch' to main-beam while not turned on. Should I use an LED in this position? It's up to you, but I wouldn't want the additional brightness of an LED when I'm driving on unlit roads at night. Also with column stalks as said above you can tell at a touch if you are on main beam, and I suggest you would need to be driving a very long time after switching them to main beam to forget to dip when you see approaching traffic.

    Headlamp Flasher:

    Optional as part of the indicator switch on Mk1 cars, standard after that. Until the dip-switch was moved to the column stalk for the 1970 model year the headlamp flasher was powered from the brown (unfused) circuit, but it should be relatively easy to add a fuse. After that they were powered from the purple fused and always live circuit.

    If your lights fail while you are driving at night, and if you have the presence of mind when suddenly plunged into blackness at 60mph on a mountain road, try the other beam (dip to main or vice-versa) or pull on the headlamp flasher. Because the headlamp flasher gets its supply from a different source it bypasses any problems in the main lighting switch or dip switch. It may just be enough to enable you to bring the car to a safe halt.

    Trim Ring:

    Clearance to wing

    If you have done any work involving removal and refitting of the front wing or any headlamp components, I would strongly recommend you leave the rings off until successfully passing the headlamp alignment test in the MOT or remove them yourself beforehand, likewise if taking it somewhere for headlamp alignment for other reasons. You don't want some scruffy oik in a garage levering them off.

    The theory is that the top is retained by two lips on the headlamp bowl, and the bottom by a spring-clip attached to the bottom of the bowl that rests in the curve of the trim ring when fitted. The clip is supposed to slide out of the curve as the bottom of the ring is eased forwards, however open to all the weather the clips and the trim ring can rust and make this extremely difficult. Going by the Parts Catalogues all MGBs had the same trim ring regardless of year - 57H 5296, although late models seem to have had rings with notches in to allow for adjustment without removal.

    Some years ago I replaced one of the bowls on Vee as it had rotted, and the replacement from the MGOC came with a screw fitting instead of the spring-clip. This is standard for cars using the same headlight like the Mini, which has a screw-hole in the bottom of the ring (one of the Parts Catalogue drawings does show such a screw, but this must be an error as the part number is the same as the others), however there is no access to such a screw on the MGB. Fortunately the spring-clip on the old bowl was reusable and I could change them over. Subsequently I worked on a car with aftermarket Wipac plastic headlamp bowls that also had the screw, but no option to replace that with a clip as it was a one-piece moulding. But the screw had been fitted to the bowl before the ring, and adjusted such that the head just fitted into the curve of the ring. Careful adjustment is needed to get the screw just right so the ring doesn't fall off (screw in too far) or jam (screw not in far enough), but get it right and it is easier to get the ring off and on than the original spring-clip.

    But back to the original arrangement. There seems little option but to lever the bottom of the ring forwards somehow until hopefully it pops off the spring-clip at the bottom ... but that has never happened for me. Brute force has been needed to pull the bottom of the ring off the clip which bends the clip forwards and it has to be pushed back again to refit the ring, with the risk of eventual fracture. Pressing down hard on the top of the ring with the other hand can help, until you can see what is going on inside. Tackling Vee's which hadn't been moved for about 10 years or so I could see that instead of a recess in the spring sitting on the rear edge of the trim ring, the end of the spring had lodged behind a lip on the rear edge of the ring. This means that instead of the ring sliding off the clip as the ring is eased forwards, the clip has to be bent right forwards, severely distorting it. With the bottom pulled forwards this far I did then try levering the ring upwards to get the top of the ring unhooked from the two lips at the top. I could get the one side off but not the other, so had to resort to putting a small screwdriver through the gap at the bottom and levering the clip up off the ring, but as often as not the screwdriver slips off. I put fresh Waxoyl on the back of the ring and on the clip and tried refitting it with the recess of the clip sitting on the rear edge of the ring, but as soon as I pushed it home the end of the clip dropped down in front of the rear edge of the ring just as before, and trying to remove it again even with fresh Waxoyl I was back to square one. I then tried pushing the spring as far back and upward as it would go, and this time the recess in the clip did stay on the rim of the ring. This did make it easier to remove, although still required some force, and pulled the spring downwards and forwards again, so had to be pushed back and up again before refitting. If there were a small cut-out in the rear edge of the ring such that you could rotate the ring to line that up with the clip it would make life easier, and indeed some of the rings in the Parts Catalogues do show a cut-out in that location, but again the part numbers are the same as before. It's possible that the design was changed at some time, but kept the part number as the change was so small and it was fully backwards compatible. But replacement rings bought in 1990 for Bee do not have the cut-out. However you get the ring off, daub the back of the ring with Waxoyl to protect that from rusting through from the back as well as to aid fitting and removal, and daub the spring-clip as well.

    Combined trim-ring puller and beer-bottle opener! December 2020
    Many years ago and occasionally since I have heard Americans talking about using a 'paint can lid remover' to get these rings off. But since I've been using screwdrivers to open paint cans for the past 55 years I couldn't imagine what they were like and how they were any better, and there were no images and precious little internet in those days. More recently a pal in Philadelphia happened to mention it, and asking him about it he made a video to show what it was like and how he used it, and because I was interested he very kindly sent me four. Initially I had Googled 'paint can lid remover' and although there were a few of a similar design in the UK for a couple of pounds the end of those was basically flat and not much different to a screwdriver, whereas the American ones are almost a right-angle at the end. Then I found them on Amazon UK, but they are supplied from the US at £10 including P&P which is quite pricey. The bonus feature of this ring-handled type is that they can also be used to open beer bottles!

    I start off at the side but because the end is bent at a right-angle the ring can be pulled forwards rather than levering against the wing. As the lower half of the ring comes forwards, the tool is moved down and round to pull the ring further forwards at the bottom.

    With the ring pulled forwards 1/2" or so the clip is visible, but trying to lever it up off the ring with a screwdriver doesn't work as it just slips off nine times out of ten. Brute-force has to be used which bends the clip right forwards, and it has to be pushed back again to refit the ring. How long it would stand up to that treatment without fracturing I don't know.

    The difference with this tool is that with the end angled upwards under the clip it can be levered up from the ring very easily, the clip is not bent, and the ring just snaps back into place when refitting. To check it wasn't a fluke I tried it on the other side of Vee a couple of times with the same result. I haven't tried Bee yet as I'm not expecting to have to remove the rings any time soon, but on Vee with the new uprated headlights they may need adjustment at the next MOT. Nevertheless I shall keep one in each car - just in case.

    Without a tool such as the above there seems little option but to lever near the bottom of the ring with a screwdriver using the curve of the wing as a fulcrum, and a thick pad to protect the paint. Note that sound wings are required to perform this manoeuvre! Then use brute-force to pull it off the clip. It's the only method that worked for me for 30 years, fortunately not a frequent operation.


     : Even though I used the tool previous 'brute force' had obviously taken it's toll as removing one of Vees the end of the clip snapped off, but replacements clips BAU1460 are available on only take moments to replace ... once you have removed the lens and reflector, inner bowl from the outer bowl, and the outer bowl from the wing ... Note that once the spring has been detached the inner bowl should rotate off the adjuster screws without needing to remove or alter the position of those screws, which avoids upsetting the beam alignment.

    Clearance to wing: October 2021:
    Graham Moore on the MGOC forum has been having problems fitting new trim rings as part of his restoration because there is insufficient clearance to the wing at the inner edge. I've had the same problem on Vee with what are probably original rings, and so has a PO as the passenger side ring is slightly flattened in that area. Measuring old and new rings - the thickness of the flange where it contacts the rubber gasket - Graham's old rings were 2.8mm and new 4.5mm. I have an old set from Bee replaced 32 years ago and they and the original ones on Vee measure 2.6mm. Bee's 'new' ones measure 2.85mm ... at one point but increasing as you go round the rim to 3.45mm! Originals have a welded seam that has to go in the area of the bottom inner corner limiting scope for placing a thinner prt by the wing, but modern ones have no weld so can fitted with the thinnest section in the smallest gap. Graham is handy for the MGOC shop and early CB wings (wide spaced sidelights) have plenty of clearance between rim and wing - 3-4mm, all the later ones had less than 1mm. He also spoke to the workshop who confirmed that they never fit later cars, and they need to grind the wing before painting and reduce the weld size right in the corner too, as well as slotting the holes in the bowl so that can be slid across to make more room. As Graham says - Great! Looking at Bee and Vee here is just enough clearance on Bee - about that 1mm Graham mentioned, and on Vee's driver's side, but on Vee's passenger side there is no clearance even having slid the bowl across as far as it will go without grinding the (freshly painted!) wing, and the ring has been flattened in that area as well.

      Whilst only originally provided for North America during the last year of production a number of UK suppliers have the headlamp ring with cut-outs for adjustment meaning removal of the ring is not required. On-car they do look a little 'odd' though.

    Headlamp Adjustment:

    First, remove your trim-ring! With the possible exception of later models (which may have a notch in the ring to allow for adjustment without removal) these can be a right pain.

    And now for the adjustment! By comparison with trim-ring removal it is simplicity itself. The adjuster screw at the top tilts the beam up and down, and the one at the side moves it from side to side. You can adjust the beams without the aid of a beam-setter if you have at least 37ft 8 ½ inches (25 ft plus the length of the car!) of flat and level surface back from a vertical surface such as a wall or garage door. Drive the car up to the vertical surface and mark the position of the centre of each headlight e.g. with electrical or masking tape. Now comes the confusing bit. Various sources now say to place two more marks 3" below the centre of the headlight, or 2", or 1" down and 1" to the left, and others just seem to use the original marks. has a diagram showing that the datum lines should be 0.5% to 2% down, and 2% to the left, which for MGB headlights typically 24" (Vee) off the ground (i.e. less than 850mm or 33.5") equates to 0.12" to 0.48", and 0.48" respectively! Or is that percentage of the screen width and height!? The junction of the two lines ('break' point here) should be between 0.5% and 2% below the headlight centre, and between 0% and 2% to the left. In the past I have set mine using the centres and they have failed the MOT as being too high, and what has passed puts a pool of light just a few feet in front of the car on dipped beam, and still on the road albeit further forward on main beam i.e. to me too low. So probably better to err on the side of lower rather than higher. The MOT should check them with someone sitting in the drivers seat, so if you do yours with the car empty (beautiful/handsome assistant not being available/willing) that will give you a bit of a margin.

    Back up so the front of the car is 25ft from the vertical surface and turn on the dipped beam (obviously doing this at night is preferable!). Each dipped beam should have a flat and horizontal top edge on the right-hand side, and the left-hand side should be angled upwards, this upward angling lights up the left-hand side of the road. Note that other European countries don't have this which is why they don't need beam deflectors when driving here like we do when driving there. A typical MGB won't have a sharp cut-off at the top of the beam like many modern cars do, having some upward scatter, but there should be a visible point where the horizontal part joins the angled part - the junction. Adjust the headlamps so that this junction is on your secondary marks. Switch to main beam and the centre of the beam should also be on these secondary marks. Note that if your reflectors are cloudy, bulbs old and blackened inside etc. the junction may not be clear enough and it can fail the MOT. Any misalignment of the bulb, reflector etc. could result in one beam to be correctly adjusted but the other not, with the same result.

    Headlamp Mounting: January 2017

    The headlamp glass and reflector (a single unit) is clamped into a chrome-plated surround with four small screws. The rear half of the surround has a tab at the top and one on the outer edge for the special beam adjuster screws to slot into. These screw into nylon sockets fitted into the headlamp bowl, and as they are turned move their part of the surround plus headlamp assembly back and fore to get the correct height and side to side adjustment. The back of the reflector should have a tag with a hole, and a spring goes between this and a similar tag inside the bowl, to pull the headlamp assembly plus clamp ring into the bowl, and it is pushed out against spring tension by the adjuster screws to get the correct beam adjustment.

    The bowl attaches to the wing with four screws - top, bottom and at each side, with a rubber gasket between bowl and wing. The gasket has sleeves for the adjuster screws, to prevent dirt being thrown forwards onto the headlamp and down the outside of the wing as well as to protect the screws from the worst of road dirt to some extent. The four bowl screws go into a reinforcing/mounting ring which is spot-welded to the back of the main body of the wing. This reinforcing ring does not appear to be separately available for the MGB, but should be the same as the classic Mini item which is part No. 14A6993 from many sources.

    Uprated Headlamps

    Relays and Fuses
    Uprated Halogen


    Relays and Fuses:
    Main beam/flasher problems
    The full current for the headlights is fed through the main and dip switches. Not only does this involve considerable lengths of wire and several connectors, but ageing switches can be less than perfect, all of which produces less light from the lamps and heat in the switches, in extreme cases melting them and causing total loss of lights. Uprated headlights almost certainly take more current which will make the foregoing problems worse, and you will not see the full benefit of the extra power. Always consider fitting relays with uprated lamps, which will result in more power at the lights and less strain on the old switches and connectors. Two relays will be required - one for the dipped beam and one for the main. The difference can be remarkable, as seen with a set I fitted to a car with uprated headlamps. Beforehand when switching from dip to main and back again there was a finite period when there was virtually no light at all! Afterwards the switch was near instant, and the lights were significantly brighter as well.

    The next consideration is fusing. The headlights were never fused by the factory. Because you are adding wiring it does make sense to fuse it, but simply providing one main fuse (e.g. the MGOC and Moss kits) could result in total loss of the headlamps if it should fail, so think in terms of providing one fuse per beam as a minimum if not one per filament. This will protect the wiring from just after the relays out to the lamps, but still leaves the relays and wiring to them unprotected. By positioning the relays close to the point at which you pick up the supply from a brown connection point and properly routing and harness-taping you can minimise the risks but some might still want to fuse the main supply as well. In this case you should use a rating at least double that for the filaments, otherwise a problem by one headlight could blow the main fuse and not the filament fuse. I would recommend using 10amps per filament or 15amps per beam, which is about double the typical current flow, and 30amps minimum for the main fuse. That may seem high, but the headlamp flasher needs to be considered. From 1970 when the dip-switch was on the column stalk the headlamp flasher used its own fused supply, but with relays all that circuit does is operate the main beam relay. If the headlights are on dipped beam and the stalk is pulled towards you to flash the main beams, both relays will be operated and all four filaments will be powered, so any main fuse will be carrying getting on for 20 amps, and needs to be in excess of that. If you are not using a main fuse in series with filament or headlamp fuses then the filament and those fuses can be standard 17/35s.

    Click on the link for the schematic and suggested layout. The standard wiring on most MGB has two double bullet connectors by the right-hand headlight one for dip and one for main. These have three wires - a supply wire and another wire in the main harness that goes across to the left-hand headlight, the third wire from a tail going to the right-hand headlight. At the left-hand headlight there are two single bullet connectors each with a wire from the end of the main harness and a tail leading to the headlight. Early cars have this junction in the middle of the car with two long tails - one to the left and one to the right. Position the fuses close to the relays. One fuse per filament will see four fuses on the output of the two relays, one fuse per beam will see two fuses feeding power to the relay. To avoid cutting into the harness, and to make the changes easily reversible if required, make up a sub-harness that picks up the blue/white and blue/red wires from the main harness via two single connectors and routes them to the relays, two wires from the relays to the fuses, and four wires from the fuses back to four single bullet connectors to join up with the wires to the headlamps.

    October 2016: Relay kits are available from MGOC and Moss Europe (with the latter being a lot more expensive!) or Moss US. Both kits only seem to include a single main supply fuse, which should it blow will kill both dipped and main beams. Daniel Stern Lighting recommends one per relay, and this kit from Advance Autowire has one per filament, but no main supply fuse, so opinions obviously vary! For both MGOC and Moss kits it would be easy to add a second fuse and have one per relay, and not much more work to add one per filament, just by adding in-line fuses with the appropriate spades and bullets. However note that the Moss and Advance kits use relays plugged in to sockets. There are two configurations of relay terminal, and with sockets you have to use the correct configuration, more info here.

    November 2020: In the space of a couple of days I was asked for advice about improving the electrics with relays and fuses from two separate people, and a pal in America sent me a picture of heat-damaged wiring at his lighting switch. All of which set me off thinking about Vee's headlights as we do occasionally use her at night.

    But first I decided to see just how much difference a relay might make. I took a length of the heavier gauge wire that is used for headlights, put a bullet on one end and fitted that to the spare hole in the main-beam bullet connector by the right hand headlight, and positioned the other end (which happened to have a ring terminal) by the battery terminal post in the engine compartment. Turned on the headlights as normal, then tapped the ring connector on the battery terminal post. Not only did they brighten significantly, but the connection even sparked confirming that significantly more current was flowing, and the voltage at the headlight bullet increased from 9v to 11.5v (engine not running), and that despite my 'ring main' wiring of the brown circuit. So Something Should Be Done.

    Relays are simple enough, but what to do about fuses? Two relays plus four fuses is going to take up quite a bit of space on the inner wing, all need mounting, and I don't like drilling holes. You can get sockets for plug-in relays so I looked for a socket for a pair of relays with a single mounting point without success. But along the way I found this dual relay with single mounting point from 12v Planet which is just the ticket - or so I thought. These are unfused and whilst I could get fused relays for individual sockets they take modern blade fuses which means carrying spares. In the end I decided to go with in-line holders that take standard fuses, 20 amp rated with spade terminals also from 12v Planet, and use just one per relay i.e. one for the dipped beams and one for the main, and expect to have the presence of mind to switch beams if the one should fail. I'm planning on having only about 6" of wire from the relay to an existing brown circuit connection. Four of these fuses could be used one per filament if you prefer but you would have to join two together to connect to the relay output, in which case the 'bare ended' type would probably be better for you to attach your own terminals.

    Fabrication went well but with five headlight-grade wires going to the two relays I discovered the individual relays were getting dislodged in the dual case during installation. They are 'skeleton' relays, the only casing is the dual case, and they are only 'clicked' in. As well as the risk of mechanical damage I can't see anything stopping moisture getting in and causing problems, so I decided to super-glue them in ... and of course ran out of adhesive and had to order more. But the biggest headache by far was getting them working properly. You need to find the supply wire to the 4-way bullet connector at the right-hand headlight and pull that out, as that becomes the relay 'operate' wire, and the output wire from the relay goes back into the 4-way bullet connector to power both headlights. In theory one pulls one of the main harness wires out, and if both sides stop working you know you have pulled out the supply wire, so you put that into a new 2-way bullet connector with the relay 'operate' wire. But if only the left-hand headlight goes out you have the wrong wire, so put that one back and pull the other one out. Easy, no? No! I just couldn't get them to work right - one beam worked but not the other, sometimes one of the relays buzzed, if the dips were on and pulled the stalk back to flash the dips went out and all sorts. Thinking I had the wrong wires I juggled them about which just confused the issue. Resorted to a 12v jumper lead to operate the relays and power the lamps directly to try and work out what was wrong to no avail. Got a meter to measure the voltages and got some very strange readings. Eventually I used the jumper wire to connect an earth to the relays on top of the existing earth wire, and suddenly they started working. When I removed the front fog/spot lights for painting and decided not to put them back I left the relay in place with just the earth wire connected having removed the other three wires. Mounting the dual relay in place of the single I simply swapped the earth wire over to the new relays 'assuming' it was a good earth ... and of course it wasn't! Testing it with an ohmmeter it drifts about a bit, it comes out of additional wrap on the harness so where it goes back to I have no idea. All I can say is that the old lights worked - probably because it was just one relay, but two sharing a poor earth get unwanted interactions. Anyway, I abandoned that wire and fabricated a new one to go under the relay fixing screw. Phew.

    At the same time I've decided to uprate the H4 bulbs to Osram Night Breaker Silver which are claimed to be about 100% uprated (see below). Incidentally, one person reviewed these bulbs and complained about them giving an 'amber' light instead of 'silver' as on the tin. The word 'dipstick' comes to mind.

    Main beam/flasher problems: October 2021 Note that if your speedo contains the main-beam tell-tale as well as the panel light bulb the speedo must be properly earthed. Brian Wall on the MGOC forum reported a strange problem affecting the headlamp flasher after doing some work on his relays. It took a couple of goes to ascertain what was happening but I suspected speedo earthing affecting the main-beam tell-tale. The first symptom was that if the tell-tale was unplugged the headlights worked as they should, and if the tell-tale bulb holder was earthed with a separate wire that also worked as it should. Subsequently Brian wrote "when I turn on headlights it will show main beam and allow me to change to dip beam, but then will not change back to main or even flash the lights (unless I) turn lights off, then on again and same sequence all over again, until I disconnect the telltale and let it hang free and then the headlights and flasher work as normal". This confirmed speedo earthing as the problem to me, and connecting an earth to the speedo allowed everything to work as it should, The problem occurred for the following reasons:

    • With the parking lights on, the lack of earth to the speedo means that the panel light is trying to earth backwards through the main-beam tell-tale bulb.
    • Without relays the two bulbs in series would earth through the headlamp main beam filaments, but the current is so low you would not notice it at the headlights. Both panel and tell-tale bulbs would only glow dimly - unlikely to be noticed especially in daylight.
    • With relays the relays only supply power to the headlamps themselves, the main-beam tell-tale is powered from the dip-switch/headlamp flasher switches as before, which are also powering the main-beam relay, hence there is a connection between the tell-tale and the relay winding.
    • When the main beam is turned off there is enough current flowing from the parking light circuit through the panel light bulb and backwards through the tell-tale bulb in series to the relay winding to keep the relay operated ... unless the panel light dimmer is turned off!
    • This keeps the main beam illuminated, but again you would have to look closely to realise it unless you were in the dark, especially if the dipped beam was illuminated.
    • The headlamp flasher used on its own, i.e. with the main lighting switch off, would almost certainly work normally. Even the tell-tale would work almost normally as current from the headlamp flasher switch would flow through the tell-tale bulb and backwards through the panel light bulb to the parking light circuit, and from there to earth through all the parking light bulbs in parallel, again unless the panel light dimmer switch is turned off.
    • LEDs used in panel lights and/or the tell-tale would change the symptoms because they will only pass current in one direction, not both like a filament bulb. LED headlamps were in use on this car but I don't think they would have an effect, and relays shouldn't be needed with LED headlamp bulbs anyway as the current is much lower.

    Uprated Halogen: There are H4 halogen bulbs available with claimed 20% to 200% more brightness for the same wattage as originally e.g. 60/55W, all road legal. There are also 100/80W and 130/100W versions for sale, but unless they were original equipment on your car they are not road-legal. The 'brighter for the same wattage' bulbs achieve that by a different design of filament which draws the original current, and hence are the same wattage (Watts being Volts multiplied by Amps), but as with anything else you don't get owt for nowt and the 'cost' (in additional to higher price) is a shorter life. For example the 150% is said to have half the life of the 130%, which itself will have a reduced life from the 110%, and so on comparing 110%, 50% and standard. When buying these make sure they are dual-filament for main and dipped beams, as there are single-filament variants which have the same H4 fitting. They are for cars with dual headlights such as the ZS which has main and dip in the outer headlight, and an additional main beam only in the inner headlight. As ever shop around, for example Halfords has a single 50% brighter at £17 (although you may get a BOGOF offer), whereas Euro Car Parts has pairs of Osram 115% at £15, Phillips 130% at £18, and Phillips 150% at £21 (although with these last two there is no written indication of whether they are single- or dual-filament). Standard halogen dual-filament are typically £3!

    November 2020: As part of installing relays and fuses I also purchased a pair of '+100%' uprated bulbs but as the detailed text says 'up to' that can mean anything or nothing. After fitting just one it's true they are a bit brighter - but not as much improvement as from the relays, I doubt you would notice the difference with two in and on the road. But they were reduced from £17 to £12 so I can live with that.

    But before considering a change such as this, it would be best to investigate your switches and wiring to see how much voltage is being lost before it gets to the bulb, if not fit relays and fuses. Clean bullets and connectors always help, and you should consider replacing the connectors at the front of the car, polishing the bullets with fine wet-and-dry or emery cloth, and reassembling with Vaseline. I did that on Vee as a matter of course towards the end of her restoration, as well as polishing all the bullets by the pedal box and in the boot, and found the indicator flashing rate afterwards was noticeably faster and more consistent even though the switches and wiring were as before. To measure the volt drop connect a meter between the brown at the fusebox, and the back of each of the bullets by the off-side headlight, for each beam when powered. No need to run the engine, although the voltages you will see will be higher the relative differences will be the same, and it is those we are interested in. There should be two wires from the harness, and one wire from the sub-harness going through the inner wing to the headlight. Any difference in voltage between the three bullets shows that voltage is being lost in that connector. And the difference between the highest of those and the brown at the fusebox is what is being lost in the main lighting switch, dip-switch, and their wiring. You can also unplug the alternator, and move the meter probe from the brown at the fusebox to the thick brown in the alternator plug, and the difference between that and the fusebox reading will tell you if any is being lost in the connections at the solenoid. Unless you have brand-new wiring and switches, and perfect connections, you are bound to see some voltage being lost, in which case your headlights would benefit from having relays and fuses installed. I fitted relays and fuses for someone with (illegal) 100w bulbs, he said before that as well as not being very bright before, when switching between dip and main the 'new' beam only gradually came up after the 'old' beam went out, leaving him momentarily in the dark. Afterwards he said they switched almost instantly, as well as being noticeably brighter. Checking Vee main beam lost volts is about 1.8v and dipped about 1.5v, with Bee (old bullet connectors at the front) a couple of tenths higher. There is only about 0.1v difference between the fusebox and the alt plug on both. Powered normally, then adding a thick jumper wire between the fusebox and the connectors (simulating a relay), there was a visible increase in brightness. Pondering.

    March 2021: Ink barely dry and they change the rules again. From 22nd March halogen to LED conversions on cars first used before 1st April 1986 will be legal. But then they go and mess it up by writing:

    Should a vehicle be presented for an MOT test with conversions before 1 April 1986 they must not be failed with immediate effect.

    Vehicles presented with converted halogen headlamp units first used on or after 1 April 1986 will continue to be failed.

    Which surely implies that only if the conversion was done before 1st April 1986 will they pass the MOT, which is nonsense. Surely it should say 'Vehicles first used on or after 1st April 1986 ...' will be failed.

    Another cock-up: "From 22 March 2021, we’re changing these rules so that not all motorcycles and vehicles will fail the MOT test if their halogen headlamp units have been converted to be used with HID or LED bulbs." This seems to exclude older sealed beam installations from being converted legally, surely 'halogen' should read 'incandescent' or 'filament' i.e. treat sealed beam and halogen the same. Even more complicated where sealed beam have already been converted to halogen!

    Even more interesting is that HID conversions will also be legal, and having been disappointed with an LED conversion I'll be looking at HIDs.

    1st January 2021: MOT rules have been changed to fail cars with LED headlamp conversions:

    4. Lamps, reflectors and electrical equipment
    4.1. Headlamps
    4.1.4. Compliance with requirements
    "Existing halogen headlamp units should not be converted to be used with high intensity discharge (HID) or light emitting diode (LED) bulbs. If such a conversion has been done, you must fail the headlamp."
    The irony is the phrase 'Existing halogen headlamp units'. Most MGBs came out of the factory with non-halogen headlamps, so even this has created another 'grey area', they probably should have used the term 'incandescent' instead.

    October 2020: Information on legality or otherwise from Classic Car LEDs and the Federation of British Historic Vehicle Clubs here.

    September 2020: Brian Wall on the MGOC forum asked about his club-supplied LED headlights and why the headlamp flasher wasn't working when the dipped beams were on. I wondered whether this was something to do with having LEDs and asked if the tell-tale was coming on. It is, so yet another undocumented feature of dual 'filament' LEDs. However Brian raised this again in November 2021 after having rewired the relays, and this time I suggested he double-check that the dip relay is remining operated and the main relay operates as well when the control is pulled to flash. And he discovered that he had cross-connected the two some how, and correcting that they work as they should.


    Intrigued by an advert in Enjoying MG I did some research and found some with the same manufacturers designation elsewhere at about half the price. They turned out to be slightly different physically as the driver module is integral with the lamp, which has a short cable terminating in a 3-pin plug which is compatible with the harness socket. There is quite a large 'lump' on the back of the 'bulb' which made me wonder if it would all fit in the bowl, but it did. The MGOC items are shown with an external driver module, as well as having the lump on the back and cable with plug so even more to fit in.

    One issue with installation is that you install the H4 adapter to the reflector/lens assembly, then slide the 'bulb' into the adapter, and twist it to get the correct beam pattern with a ball-bearing dropping into a hole to hold it in the selected position. This is so that one kit can be used for both RHD and LHD with the upsweep on the correct side ... but there are a whole series of holes all round the adapter meaning you can select any of about a dozen positions, including with the beam vertical instead of horizontal! The 'issue' was with the rubber seal that fits round the base of a halogen bulb and pushes up against the back of the reflector. With the LED items you fit the rubber seal to the back of the reflector after the H4 adapter, then push the LED 'bulb' through the hole in the seal into the adapter. However the seal is too deep to allow the 'bulb' to go in far enough for the ball-bearing to engage with one of the holes, meaning it (the seal) would have to be cut down. I didn't do this, pending further enquiries.

    As far as adjusting the rotational position of the 'bulb' goes this has to be done with it powered, but before the lens/reflector is clamped into its carrier. The flat and angled cut-offs of the dipped beam can be clearly seen in the glass, and as my glass has similar moulded lines, it is a simple matter of turning the 'bulb' until the edges of the beam line up with the mouldings in the glass. Bear in mind that when looking at the glass, everything is reversed compared to how the light strikes the road, i.e. the light is at the top of the glass instead of the bottom, and the angled section is on the off-side instead of the near-side.

    That gives rise to another 'issue', and that there is a distinctive 'dead' area in the light at the top of the glass, which means there will be a similar 'dead' area on the road right in front of you. This can be seen in YouTube demonstrations of other LED installations on other vehicles, and isn't apparent with halogen bulbs or sealed-beam units. The light is very white, and makes the tungsten pilot light in the rubber-bumper headlamp assembly look like an orange neon. A brief test at night in lit streets didn't seem to give that much better actual visibility, it was more the whiter reflection.

    Yet another issue was flickering. A pal has had two sets of LED stop/tail but they failed the MOT being 'adversely affected by the operation of other lamps' i.e. flickering when the (incandescent) indicators were in operation. Some have said that is a factor of cheap bulbs, and if you pay more for better quality from other vendors it doesn't happen. One such vendor was named, and this is who I got my LED headlights from. Interested to see what happened when I cranked the engine with them on, I couldn't help laughing out loud when they cut out altogether apart from very brief flicks of light. There was also a visible flicker when the indicators were going - so much for 'better quality'.

      However the biggest issue concerns legality. It wasn't until I got them that I saw on the box 'OFF-ROAD USE ONLY', despite the vendors description including words such as 'as used on our cars' and 'not dazzling other road-users'! So I did a search for 'off-road' in their ad and found buried in 2537 words of Terms and Conditions the statement "... Therefore all our external LED bulbs are sold as off-road use only." The MGOC ad makes no mention that I have been able to find, and speaking to them it is a grey-area. 1986 Regulations state that cars first used from 1st April 1986 must have filament lights with an approval mark, which is fair enough. But for cars used before that there are contradictions with the UN accord of 1958. The upshot is that pre-1/4/86 it's not clear (no pun intended). You are unlikely to get stopped by the Police, and the MOT only checks function and adjustment not legality, but that still leaves your insurance company. I consulted mine, and they were quite clear that they did not approve them, and it could compromise any insurance claim even if I had advised them beforehand. I'm pretty sure he knew what he was talking about as he was a Land Rover enthusiast and said there were LED conversions for Defenders with 7" lights which were legal. He gave me the details of two types (Nolden 7" Bi-LED and Lynx Eye) but these are so aesthetically different (and expensive!) compared to the MGB originals they are out of the question. The upshot is, these LEDs go back, and uprated (brighter but same wattage, higher wattage also being illegal) halogen are next to be tried.

    The doubt over the legality of external LED lighting has cropped up before on MG fora, and many pooh-pooh it. But that's up to them and you. If you make an informed decision to fit them and it goes wrong, you have no-one to blame but yourself.

    HID: June 2021: From 22nd March halogen to HID conversions on cars first used before 1st April 1986 will be legal. But having specifically banned LED and HID conversion from 1st January 2021 then allowed them in March, they have confused the issue by referring to 'halogen' instead of 'filament' or incandescent'. Does that mean sealed beam i.e. non-halogen can't be converted? And what about cars that were originally sealed beam that have already been converted to halogen? Nevertheless as Vee IS halogen and we do use her at night I decided to look into a conversion.

    Switch Connections:

    Only three wires on dash switches but still several permutations even with only three spades as on rocker switches. These can fit in the dash either way round but forward-facing lamps have the logo pointing to the right. Later illuminated rockers fit with the illuminated panel at the top. Toggle switches can have several unused spades and also work either way up, although there should be a flat which ensures they cannot turn in the dash as well as meaning they can only fit one way round. If the terminals are numbered then brown should go on 4, red on 7 and blue on 8. But you can derive the connections by using an ohmmeter as follows:
    • When off all three spades should be isolated.
    • In the first operated position two spades will be connected together, brown and red can go on these either way round.
    • In the second operated position a third spade will be connected to the other two, blue goes on here.

    'Lights on' warning:

    A simple 'lights on' warning buzzer when a door opens which avoids having to cut one of the courtesy-light switch wires, but operates from the passenger door and manual switch on the courtesy light as well. By cutting the purple-white to the drivers door switch a diode can be inserted so only the driver's door operates the buzzer. The polarities of the diode(s) and buzzer assume a negative-earth car, they should be reversed for a positive-earth car. Any 100v, 1 amp diode and 12v dc buzzer should suffice.

    Added April 2010:

    I've been asked by Frank Mooring if it's possible to use the existing North American spec seat-belt and 'key in' warning buzzer for a 'lights on' warning, rather than provide an additional buzzer. I suggest schematics (click the thumbnail) for each of the three types although I haven't been able to test them. This requires the use of a relay to convert the light-on signals so they can be used by the existing circuit. It may be easier just to provide and additional buzzer, but this will need a diode as shown in the schematics above.

    Daytime Running Lights (DRLs):

    Ubiquitous now, and getting so bright there has to be a risk that cars without could be missed (which is also why you see many motor bikes running with headlights on). There is enough chrome and bright-work twinkling on the front of your average MGB in sunny conditions, but in dappled sunlight under trees and going from sunny to shady and back again it would be easier to miss dark-coloured cars, such as Black Tulip!

    Legally, there seems to be no information regarding after-market DRLs, and even that for later vehicles where they are original equipment is sketchy to say the least. The MOT Manual Section 4.2 says they are only inspected on vehicles first used on or after 1st March 2018, and the only mandatory information for those is that they must go on and off with the ignition. After that whether they go on and off with other lamps is covered by 'may or may not', and even "If position lamps are combined with direction indicators, position lamps may or may not switch off when the relevant direction indicator is flashing". They are not mentioned in the Categorisation of vehicle defects for passenger cars, and I can't find any mention of lighting at all in the Construction and Use document ... which is because it is covered under the separate Road Vehicles Lighting Regulations, which says even less than the MOT Manual.

    LEDs are the obvious choice for longevity and low power consumption. I spent some time looking at these, but for after-market you are looking at spending £50 upwards without knowing anything about how they perform. Avoid cheaper 'styling' lights, they use much smaller and less bright LED elements. I even pondered OEM types as at least one can see those in use on our streets, but usually they are highly 'styled' for integration with existing bodywork on the car in question and not suitable for aftermarket use - round MINI types being an exception, but they are going to cost a fortune, maybe even at a scrapper.

    Which led to the next question - circular or strip? I did find some cheap circular 9-element ones that fitted quite neatly to the honeycomb grille, but they were just not bright enough. Then after a long time with occasional searches of the internet I came across these Eagle Eye LEDs. Reputedly 9 watts (although I've never been able to get a clear explanation from any supplier of just what wattage means as far as LEDs go) and with a lens at 13mm diameter (overall housing diameter 22mm) much bigger than anything else I had seen before. At £2 (free P&P) for a pair on a slow-boat from China it was definitely worth a punt and when they sailed (OK, that's enough) through my letterbox a couple of weeks later the good news was that they were very bright indeed across the whole of the lens area, I couldn't look into them, definitely suitable. The bad news was that one of them didn't work. But an email to the vendor elicited a very polite apology and another pair sent. Take care when considering other suppliers, some of which supply in larger quantities with a lower unit cost, as there are smaller, and less powerful, versions around e.g. 3W types at 13mm overall diameter. Read the descriptions and look at the images carefully - compare the overall and nut/thread sizes, this supplier was the only one I could find at the time with this physical size and power that would ship to the UK. There were also more expensive suppliers, but for identical items, so simply paying more for the same thing. Some of these are probably based in the UK, so you would get them quicker, but for a new project I'm of the opinion that time is less important, unlike for something that has broken and needs fixing as quickly as possible.

    Next thing to ponder was quantity, mounting and positioning. Four each side should be enough, I know many OEMs go silly with a couple of dozen, but four each side is quite common and should be fine, so order three more pairs. These are individual LEDs, with an aluminium threaded body and nut, and the cable coming out of the back. The threaded part would fit through the holes in the honeycomb grille, so vertically at the outer edges is a possibility. But the grille is tipped forwards slightly, so each LED would need to be angled to point forwards (I had a similar problem with the round ones) individually, or a row of them on some kind of a strip held forward from the grille at the bottom. Then there is the question of weather. With the best will in the world even though intended for car and motorcycle use they are not going to be completely weather-proof. The (very thin) cables do go through a rubber grommet into the back of the threaded part, but who's to say that's enough to prevent water getting in? So I decided to mount them in a box. Given the size of a box needed to accommodate the threaded part, that precluded fitting them in front of the grille as they would project forwards far too much. So horizontally under the bumper it is, there is enough depth to the valance for the box, and it can be mounted to the bumper iron that is immediately below and behind the bumper in just the right area.

    The box was the next thing - long enough for four across, high enough for the 23mm overall diameter of the LEDs, and deep enough to accept the 30mm threaded part and the cable that comes out of the end. After some searching Maplin has just the job at 112mm x 31mm x 62mm. I'll need two, but order just one to start with for proof of concept. Carefully marked up and drilled the holes (10mm) - pilot first, then stepped hole cutter step by step so I could make sure I was still correctly aligned and evenly spaced. Slotted in the LEDs, fitted the nuts - and a moment's panic as I realised I hadn't taken the internal pillars for the lid screws into account when setting the spacing! Fortunately there was just enough room to turn the nuts on the outer pair. I used silicone grease as a sealant between the LED flanges and the face of the box.

    Internal wiring: Next job was to join the four cables together inside the box, and bring a single 2-wire cable out. As mentioned the cables are very thin, with the individual wires and conductors even thinner, so care needs to be taken when joining the four pairs of wires to the stouter external cable and to give mechanical support to the whole assembly. With the five wires in each connection soldered together, and heat shrunk, I turned the joins back against the sheaths of the four cables and slipped another piece of heat-shrink over the whole thing to remove any mechanical stresses from the joins. The external cable was two-wire black sheathed as used on many mains electrical appliances these days, in stock from having been chopped off various dead electrical appliances in the past. I have mounted the box with the lid on the bottom so lying water won't be able to run into the box, but this also allows me to get into the box without removing the box from the car should that be required. I also daubed silicone grease around the join between lid and box and in the screw recesses.

    Mounting to the bumper iron was the next consideration, and I decided on a strip of black plastic cut from some square-section down-pipe, under the centre two LEDs, to go up between the iron and the bumper and hook over the top of the iron. If needs be a strip of double-sided foam tape (e.g. number-plate tape) could be used to stick the faces of the strip and the iron together. I've not taken the bumper off since the restoration 25 years ago, but the six nuts came undone easily (courtesy of always reassembling everything with Waxoyl or copper-grease) and I carefully lifted off the bumper, badge-bar and number plate complete. I'd previously measured how far it was from the top of the bumper iron to the bottom of the bumper, and that gave me where to bend the mounting strip to hook over the top of the iron. It only need bending into a right-angle, with a short overlap, as the bumper is close enough to stop it coming off again. Hooked the strips over the iron, and refitted the bumper. When fully tightened the back of the bumper is close enough to the top and front of the iron to grip the strip firmly, no sticky strips needed.

    Connections to each other and existing wiring: There is a convenient space at the lower outer corners of the grille surround to fed the cable through, but not very big, so the connectors to join them together and whatever I use to connect them to the cars wiring need to be small. In the end I settle for standard bullets and connectors, even though they are less than ideal for behind the grille i.e. exposed to the weather. But Vaseline used to aid insertion will keep moisture out. I use four-way connectors, to join together the two cables from the DRLs, plus the wires to connect them to the cars wiring.

    After-market DRLs seem to come with a box of electronics so that they only come on once the engine has started and is charging and the main lights are off, and go off when the main lights are turned on. If you were using 100 watt incandescent DRLs then I could see the point of not powering them until the engine has started, so taking a significant load off the battery during cranking, but these are LEDs with very low current consumption (30mA for eight). Also reckoned I wouldn't need any relays or electronics to switch them off when the main lights (parking or head lights) are turned on. Like any other light DRLs need positive and negative connections. Positive is easy - just connect to an ignition supply, but for the negative I used a bit of lateral thinking. I simply replaced the 2-way bullet connector for the right-hand front parking light with a 4-way connector and plugged the negative wire from both DRLs into that. How can that work? With the main lighting switch off, there are four parking lights, at least two number plate lights and at least four panel lights (depending on the setting of your rheostat) each going to earth i.e. all connected to earth in parallel, which with incandescent bulbs gives a relatively low resistance path to earth. Connecting the LEDs to the parking light wire the LEDs can 'see' the earth through the parking light bulbs, and you end up with a potential divider. With the relatively high resistance of the LEDs in series with the relatively low resistance of incandescent parking light bulbs, with a 12v supply you end up with 11.75v across the DRLs and only 0.25v across the incandescents. This means the DRLs effectively glow at full brightness and the parking light bulbs etc. do not glow at all. Note this is with incandescents, with LED parking and number-plate lights the DRLs would probably be a little dimmer and the parking lights might glow a little, as less voltage would be across the DRLs and more across the parking LEDs due to the changed resistance characteristics in the potential divider.

    To extinguish the DRLs with parking or headlights on, when the main lighting switch is turned on with the ignition on, you now have a full 12v connected to the parking lights, which results in 12v both sides of the DRLs, which means they are extinguished (same principle as the ignition warning light when the engine is running).

    That leaves the situation of having the main lights on with the ignition off, which would result in 12v being connected across the DRLs but with reverse polarity, which LEDs Do Not Like. So I included a blocking diode (1N4001 or 1N4002) in the wire that connects to the parking light connector, which prevents that reverse current flow.

    I also connected the DRLs to the green circuit i.e. fused ignition instead of the white, so if there is a short in that wire it would just blow that fuse. And if the DRL wire connected to the parking light connector should short to earth, the parking lights are fused so again preventing damage to any wiring. On early cars with unfused parking lights you might want to use an in-line fuse as well as a diode in the parking light wire.

    The result is very visible, especially in low light, and anyone who misses these shouldn't be driving.

    Brake Lights:

    LED park/stop/tail lights
    Supplementary brake lights


    As factory wired.

    Switch failures
    Switch relay
    Hydraulic to mechanical conversion

    All Mk1 cars, and all RHD chrome bumper cars, use a hydraulically operated switch in the junction on the inner wing near the fusebox. Early switches 13H2303 had screw terminals, later switches C16062/SMB422 use 'Lucar' or spade terminals. Replacement switches of this type seem to be problematic in that they cannot handle the load of the lights and premature failure is often reported, sometimes just after a few weeks, with subsequent replacement no better, meaning either a slave relay has to be installed or conversion to mechanically operated switch is needed. Note that these options are usually only needed if you have the hydraulic switch in the brake pipe manifold on the inner wing, not the mechanical switch fitted to the pedal cover or frame.

    North American Mk2 cars in 1967 had a dual-circuit system - without a servo - with a mechanical switch (BHA4675) on the front of the pedal box. RHD Rubber bumper cars up to September 76 had the same arrangement. Also reported (but less common) are complaints that replacement switches of this type can spring apart because the crimping of the metal part onto the insulator isn't good enough.

    For the 1975 model year North American cars got a dual-circuit system with a combined master and servo, and the same mechanical switch was moved to the back of the pedal box. RHD cars got this system for the 77 model year on.

    Note that in the 77 and later Leyland Parts Catalogue - Servo System - Dual Line Brakes item 22 is listed as 'BHA 4675 - Switch - stop lamp' but the drawing depicts the brake balance switch mounted under the servoed master.

    The mechanical switch needed to change position when the combined master and servo was fitted as the brake master faces the other way. Originally the pedals were pivoted below the push-rod, which was mounted at the top of the pedal, and as the pedal was depressed the push-rod was effectively pushed towards the driver, so the switch could be mounted in front of the pedal in line with the push-rod. But with the combined master and servo the unit is so long it has to face into the engine compartment. This means the push rod has to be pushed away from the driver, so the pedal is now pivoted right at the top, and the push-rod is lower down. Consequently the switch now has to be behind the pedal, again to be near the push-rod. More info on the boosted dual line pedals and pedal box here.

    The hydraulic switch only lights the brake lights when a certain amount of pressure has been developed in the hydraulic system i.e. the brakes are already being applied. But the mechanical switches light the brake lights almost as soon as the pedal starts moving, i.e. before the brakes start to be applied, and so give an early indication to following cars that one is about to brake. The hydraulic type are not adjustable, and the usual mode of failure is that they need more and more pressure before the light they lamps fully under light braking they may only illuminate dimly or not at all, but can also extinguish the lights under heavy braking. I've read one report that one of these has also stuck on.

    The mechanical type are adjustable and it is critical to have them correctly adjusted. These switches are of the 'normally closed' type i.e. when the pedal moves away from the switch to release it its contacts close and the brake lights come on, and it is only when the pedal is released and operates the switch that the contacts open and the lights go off. If the switch isn't screwed in far enough the brake lights will be on all the time. But more importantly if the switch is screwed in too far it can stop the pedal returning all the way, which can block the bypass port in the master cylinder causing the brakes to stick on as the fluid heats up and expands. Adjust the switch to give about 1/8" free play at the pedal footpad. This free-play must occur at the pedal to master push-rod pivot - impossible to see with the cover on, and impossible to measure with the cover off for the pedal-cover mounted type! Maybe the answer is to screw the switch out until the lights stay on all the time, then screw it in counting the turns and being aware of the free play, until the switch starts moving the pedal down on its own, then unscrewing the switch half the number of turns you counted. I must try it one day ...

      Updated November 2009:

    With the mechanically operated switch on the V8 I was surprised just how little movement of the actuator rod is possible - just 73 thou measured at the switch and one and a half turns between the light just going off and starting to reduce the free-play at the pedal. This shows just how careful you have to be, although setting it at three-quarters of a turn further in from the light just going off gives a good tolerance. I found mine at just one quarter of a turn, which is cutting it a bit fine. Out of interest when reset to three-quarters of a turn this gave nine and a quarter turns to remove the switch, but will vary greatly from car to car depending on the dimensional tolerances of pedal, pedal frame, pedal cover, master push-rod and all sorts.

    Switch failures:
    Protecting the switch with a relay
    Hydraulic to mechanical conversion October 2018:
    Earlier systems with the hydraulically operated switch worked well enough when new, although after many years they can require more and more pressure before they light the lamps and you may not be aware of that from the driving seat. One way is to look in your mirrors when stationary for the reflection from a car stopped behind you, particularly at night, or when backed up to garage doors, a wall etc. Alternatively you can probably tell simply from the indicators or heater fan slowing down slightly when you press on the brake pedal, especially at idle or with the engine switched off.

    Electrical failure of the mechanical switches seems to be virtually unknown even though significantly more than 50% of MGBs used them. Plungers can apparently stick if the car is not used for a long time, but once they are replaced the current Lucas ones apparently have a habit of springing apart as the metal can is not crimped onto the plastic part that carries the terminals anywhere near as firmly as the originals.

    There have been claims that using silicone fluid causes the hydraulic switches, even new ones, to fail within a very short time. Certainly from my telecom days, silicone grease was death to contacts, being a very good insulator even resisting the rubbing action as the contacts close. However it now seems that the real culprit is poor quality replacement switches failing in a very short time. If you cannot get an OE (original equipment) switch or NOS (new old stock) you may need to fit a relay to take the load of the lamps off the switch. The relay will need a quenching diode or varistor as even the back EMF generated by the switch releasing the relay seems to be enough to cause the switch to fail. The later mechanically operated type cannot suffer from the silicone fluid problem of course, but if they suffer from the same premature failures as the hydraulic type (and I've not heard of any so far) the same relay circuit can be used for these as well. Alternatively you could fit a generic switch such as this 'pull-on' type seen at Stoneleigh which can replace the pedal return spring and is screwed to the underside of the engine-compartment 'shelf' in an appropriate position, or use a suitable micro-switch with a normally-closed contact off the pedal as I have done here, as well as Herb Adler. Bear in mind generic switches must be capable of tolerating the inrush current of your lamps, which for conventional incandescent bulbs is significantly more than the current when they are fully lit, for the following reason:

    Inrush current: Incandescent filaments have a positive temperature coefficient, i.e. as voltage is applied and they start to glow, the filaments heat up which increases their resistance, which greatly reduces the current they draw (Amps equals Volts divided by Resistance) when fully lit as compared to when voltage is first applied. The wattage printed on the bulb represents the 'fully lit' current at the supply voltage, i.e. Amps equals Watts divided by Volts i.e. for brake lights 21w/12v = 1.75 amps. Per bulb, so 3.5 amps constant though the switch while you have your foot on the brake pedal. But the inrush current is based on the voltage divided by the cold resistance (as measured with an ohmmeter connected to an unpowered bulb), which for a typical 21w bulb is 0.5 ohms. 12v/0.5 ohms gives 24 amps per bulb at the instant of switch-on, i.e. 48 amps in total through the switch! That's a theoretical maximum, there will be various parasitic resistances in the switch, wiring and connections which will result in a volt drop before the lamps. The Lucas Fault Diagnosis Service Manual states that 1.25v volt-drop is acceptable for most circuits in the car (except for the starter which is 0.5v maximum). This is at the standing current when the lamps are fully lit, and Ohms Law says that a volt-drop of 1.2v at 3.5A implies a parasitic resistance of 0.35 ohms. That in series with the cold resistance of two bulbs in parallel (0.25 ohms) will give a practical maximum inrush current of 20 amps. This amount of current through the parasitic resistances will result in a volt-drop of about 7v i.e. more than half the system voltage, leaving only 5v for the bulbs (figures have been rounded and the system voltage taken as 12v even though it can be up to 14.5v when charging). However that 5v is enough to start the filament heating up, which reduces its resistance, which reduces the total current in the circuit, which reduces the volt-drop across the parasitic resistances, which leaves more voltage for the bulb. This heats it up even more, and you get an exponential rise in bulb resistance to its fully-lit maximum, and hence an exponential fall in total current to its fully-lit value, which results in a rapid shift of voltage from the parasitic resistances to the bulb filaments. Eventually you end up with the majority of the system voltage across the bulb, and relatively little (Lucas's 1.25v) lost in the parasitic resistances. However it takes a finite time for this to happen, which why incandescent lights take longer to light fully than LEDs. Even though the parasitic resistances are still present if LED brake lights are used there is no inrush current for LEDs, and the steady-state current is lower, so to all intents and purposes all the system voltage is present at the LED the instant it is powered. Also there is no element needing time to physically heat up and start to glow, and these are the reasons why LED brake lights illuminate faster than incandescent. Headlamp bulbs have an even lower cold resistance, typically 0.4 ohms at 55w and 0.3 ohms at 60w, which gives an even higher inrush current. The more powerful filament needs more voltage in order to output a given level of light, which means getting to full brightness takes longer. I fitted relays (and fuses) to the uprated headlamps on a pal's MGB, which takes a lot of the parasitic resistances out of the circuit, and the difference was remarkable. Before the relays, when switching from dip to main or back again, there was a finite period where there was effectively no light at all! After the relays the switch was near instant, and the lights were much brighter as well.   June 2011: Discovered Bee's brake lights not coming on just three days before the Ratae Run. Wary of going into the hydraulics so close to an event I found the switch was working but high-resistance - too high to work the lamps but not so high it wouldn't operate a relay to light the lamps, so installed a relay. However on the morning of the run I found that although the relay was clicking it was lighting the lamps under light pedal pressure and extinguishing them again under normal braking. I managed to wire in a switch to operate the relay manually, which got us through the day with no dramas, and changed the switch (MGOC Intermotor) next day. Imagining all sorts of difficulties undoing a 40 year-old switch it moved fairly easily gripping the multi-port adapter with channel-lock pliers and a correctly fitting spanner on the switch. Some polyethylene under the master cap to reduce leakage, had the new switch in my right hand while I removed the old switch with my left, then popped in the new one, and just a tiny dribble of fluid. Originally I was going to reuse the relay, but that wouldn't have told me anything about the quality of the switch, so I've left it in-situ but not connected. I've also connected the switch output to the overdrive lockout LED (via a couple of diodes) as a 'tell-tale' so I can see the switch operating, at least then I stand a chance of spotting it if the switch fails during a run.

      July 2013: Two years on I'm noticing quite a bit of retardation before the tell-tale comes on, and even then it is only coming on dimly until I press the pedal more firmly - not good. After our return from the Surrey Run I connect the relay that I made up two years previously, and I find that the lights are now coming on cleanly, and with the pedal about an inch higher than before, so significantly less pressure, and much lighter braking. Contact the MGOC describing the problem and asking if they are aware of problems with this switch and get the reply: "Thanks for your enquiry, unfortunately this is charactertic (sic) of this brake light design and why it was redesigned on the later cars to a mechanical system. The hydraulic switch does require extra pressure to ensure operation, assuring no air is trapped within the hydraulic system." Inaccurate as well as missing the point. So I write back re-emphasising that they seem to be coming on late, as well as dimly unless I press the pedal quite hard, and this time the reply is: "If the brake lights are coming on dimly this is normally associated with an earthing problem." i.e. still missing the point. So I write back again, keeping it as simple and as clear as possible, and this time I get a phone call saying they will send me a replacement switch, but show no interest in the 'old' one.

    It arrives in a couple of days, and it occurred to me that it would be interesting to compare contact resistance against pressure of the two switches. After a bit of fiddling around I find the conical adapter for football and air-bed inflation that comes with my foot-pump fits nicely in the hole in the end of the new switch. What's more it expands as I apply pressure, which keeps the air in. I connect my analogue multi-meter on it's ohms scale, and start pumping. I'm quite surprised to find that I go past 20, 30, 40, and 50psi before the meter moves, in fact initially it takes nearly 60psi, but at least it swings from infinity all the way across to zero, so making a good connection. Over a few operations the pressure required drifts a bit lower, and stabilises at 50psi. I repeat the operation to swap the switches on the car, again with virtually no fluid loss. Reconnect the relay straight away (I won't be running this switch without!), check the brake pedal, and they come on at full brightness with very light operation. I then connect the old switch to the foot-pump, but even though I get it up to 90psi (max for the pump is 100psi) I get no movement on the meter.


    What lies inside the first replacement switch. I cut this one open (a bit more neatly than last time). No fluid on the contact side of the diaphragm, but a different internal construction to before. However the principle is similar i.e. fluid presses against a diaphragm, which presses against a metal disc, which pushes against a spring or springs. Where this one differs is that instead of the disc moving a contact finger to make the electrical contact, with a rubbing action, the disc bridges two fixed contacts directly. I.e. no rubbing action, and even though there is only slight burning on one part of the disc and one of the fixed contacts it is obviously enough to start affecting the quality of the connection.

      September 2017: Andy Tilney posted on the MG Enthusiasts MGB Technical forum that he had found NOS Lucas brake light switches at LMS Lichfield who have tons of ex-MOD spares and other parts. However on external inspection they don't have the riveted spades like the originals, but have them going through the plastic moulding as on the poor copies. Rather dashed his initial euphoria, although when they checked their stock they found one with riveted spades, so he bought that one as well.

    I went over and purchased one and sectioned it as before, with interesting results. Whilst basically operating on the same principle as the cheap copies i.e. a disc pressed against the internal parts of the spades, they do differ in detail and also probably in the materials used which may well be enough to make the difference. However their current price is the same as the usual suspects so I'd imagine the quality is the same. Coming in a green Lucas box counts for nothing, see this warning about indicator flasher units that have hazard flasher internals!. Only red/orange Lucas boxes - ideally saying 'Lucas' in full rather than the 'L' in a stripe - are truly NOS or OE.

    If the materials in these Lucas switch is harder that may well resist burning better, so I decided to test that theory. Couldn't find the earlier failure that I sectioned, so went to try the second one from the MGOC that has been in Bee for four years ... only to find it has riveted spades! And no, I'm not going to section that one as well!!

    Made to order

    If you can't get hold of an NOS switch then given the reputation of current-stock switches the only solution seems to be to fit a relay, so that the brake light switch only handles the very small current of the relay, it is the relay that switches the much higher current of the lights. See this modified schematic and information on how to obtain a ready-made relay or make your own up.

    June 2011:

    As mentioned above, just before a run I found the switch wouldn't light the lamps but would still operate a relay, so installed one as a quick-fix until I replace the switch. However given the reputation of current (ho ho) switches I decide to do a 'proper job' on installing a relay, so it can be used permanently i.e. with the new switch. Piggy-back a green off the hydraulic switch (rather than the purple, or a fused brown) to the relay terminal 30 (one of the contacts). Use a male to female extender for the green purple taken off the hydraulic switch to terminal 87 of the relay (the other contact). A female to female to connect the output side of the switch to one side of the relay winding (85), and take the other winding terminal (86) to earth. As it will almost certainly be used with a new switch, and as I don't know how the old switch will react to the back emf when releasing the relay, I fit a diode (A Lucas diode, no less!) between the two spades which go to the relay winding terminals to protect the brake light switch contacts. Note: This is now a varistor which means that positive earth cars with this relay can be converted to negative earth without changing the circuit. There is a very handy unused earthing point on the inner wing close to the hydraulic switch complete with screw and washer, for both mounting and earthing the relay, and I have brake lights again. The only issue is that with the dicky switch the relay is often giving a double-click when it operates and when it releases, which won't be doing the bulbs any good, so I'll be changing the switch sooner than later. Sooner, as it happened as just a couple of days later about to set out for the start I discovered that although the relay was still clicking it was clicking on at light pedal pressure and off again under normal braking! However I had a little-used switch under the dash wired into the engine compartment which reached the relay, so I had manual brake lights. Fortunately hardly had to use the switch until approaching the A42 for the journey home and in traffic, the Navigator was not best pleased when she asked why I kept reaching under the dash. Once on the A42 and M42 I didn't need them until the exit slip-road, and didn't need them travelling through Solihull to home. Next day I replaced the switch. I was intending to use the relay with the new switch from the start, but that would have told me nothing about the quality or otherwise of the new switch, and if they are poor quality then suppliers need to be made aware of it. So the relay has been left in-situ but not connected, and I will be checking the brake lights before and after each run for a while. Sure enough in a couple of years I was noticing from a tell-tale I had installed that the pedal was needing more and more pressure before the lights came on, so nagged MGOC until they replaced it, and connected the relay. No more problems, but five years later decided to add a mechanical switch so they come on as soon as the pedal starts to move.

      Brake light relays made to order for the MGB as well as other makes and models.

    Uses existing connection points i.e. no cutting of wires, and can be restored to original in moments if required. Suitable for both positive and negative earth systems, just specify length of wiring from relay mounting point to switch position, and switch terminal type if they are other than conventional spades. Click the thumbnail for details. Usually despatched within 24 hours of receipt of payment.

    March 2021: If you find your brake pedal needs more and more pressure to light the brake lights then you will need to replace the hydraulic switch at the same time as you fit the relay. If you just fit a relay then the situation may improve, and the switch won't get any worse, but it is already damaged so must be replaced. Mike Robertson has just purchased one saying he replaced his switch about a year ago and it's got progressively worse so the switches obviously haven't got any better! He has another new one to fit with the relay.

    However there is another option and that is to convert from a hydraulically operated switch to a mechanically operated.

      Hydraulic to mechanical conversion - or 'seeing the light'. October 2018 Rubber bumper cars used a pedal-operated switch from the outset, which is standard practice on probably all cars these days. The main feature of these is that the brake lights come on as soon as you start moving the pedal, before there is any braking effect. For example it takes about 35mm of foot-pad movement before Bee's hydraulic switch turns on the lights, but only 7mm for Vee. Out of interest the ZS has 15mm but that switch has a much longer plunger. The MGB mechanical switches don't seem to suffer from the same problem that the replacement hydraulic switches do - I've not come across a single report of electrical failure of these, either original or replacement (however there have been some reports of plungers sticking on cars not used for a long time, and the insulated terminal plate on current stock popping out of the metal housing due to inadequate crimping). Why this should be I don't know as I haven't had the opportunity to open one up. They use the same 'soft-close' rather than 'snap-action' as the hydraulic switches, but maybe the physical design better allows for a wiping action such as the OE hydraulic switches had. There has been more chatter lately on various fora about the hydraulic switches, and people coming up with options to fit a pedal-operated switch to cars with the hydraulic switch, some using various bits of wood or drilling holes which doesn't appeal to me, but it spurred me on to see what I could do.

    To fit the factory switch either needs you to replace the pedal cover - they are NLA but may be available from one of the breakers. Or you could modify the existing cover by drilling and welding a suitable boss or nut, but the positioning is fairly critical. Another option is to fit a switch in the cabin under the bulkhead shelf, resting against the front of the upper part of the pedal, and that is eminently feasible.

    There is stiffener right beside the brake pedal, and a bracket for a switch could be attached directly to that. Not only would it be difficult to drill in that location, but I don't like drilling holes anyway. However there is a convenient welded nut for a pedal-box screw just the other side of the bracket, in a convenient position to mount a bracket, and that is what I opt to do. It just needs a longer screw, then a nut with washers to tighten the bracket against the welded nut. Oddly although this screw is one of six holding the pedal-box to the shelf it is a different size to the other five - 5/16" UNF as opposed to 1/4" UNF - possibly because it is the closest one to the brake pedal which has the greatest force applied to it during driving.

    The standard screw is 5/8" long, replacing it with 1 1/4" allows a few threads to remain exposed after a plain washer, lock washer and standard nut have been fitted. You must use a plain washer even with a stiff- or Nyloc nut or as you tighten the nut it tends to move the bracket out of adjustment.

    I chose to wrap the bracket round the flange at the bottom of the stiffener slightly to resist any attempt for the bracket to twist back from the pedal, which would compromise the adjustment and could leave the brake lights on. It does make for a tricky bending operation though, and if the part that goes across the pedal is too high it can foul the spring and make a noise as the pedal is operated and released. Subsequent thought is that a simple bend of 90 degrees under the stiffener would be more than adequate. For the second bend to make the part that bears against the welded nut, if this is slightly less than 90 degrees then as the nut is tightened it will tend to push the vertical part of the bracket firmly against the side of the stiffener to achieve the same positively located result, and be a lot easier to produce.

    I used this switch from eBay. It's rated at 15A and 120v AC, and snap-action, so hopefully OK. Switches are rated higher on AC than DC as the alternating current passing through zero 100 times per second (50 Hz has one positive and one negative pulse per second, hence passing through zero twice for a full cycle) will tend to extinguish any arc created when the switch opens. However it's not the opening current that is the problem with hydraulic switches as that is only 3.5A and non-inductive, but the inrush current on closing which is a lot higher. But as these switches are snap-action and it is the 'slow-closing' of the hydraulic switches that causes the problem, we shall see. This switch has spade terminals to which standard spade females make a good firm connection. Note that the switch needs a normally-closed contact as the switch is released when the brake pedal is pushed, and mine has three terminals to give a normally-open (not used) as well as the normally closed. Switches with only two terminals may be of the normally-open type and not suitable for this application without additional components.

    Bracket with switch and wiring fitted - pedal foot-pad travel down from 35mm to 8mm, and 5mm of that is taking up the free play in the linkage between pedal and master push-rod.

    You have a couple of options for connecting the switch to the existing wiring - I fed 2-wire sheathed cable though the main harness grommet - and there is also the question of what to do about the existing hydraulic switch i.e. leave it connected as a 'second string' or take the wiring off that and extend it to the new switch. I decided on the latter option, and if you don't have a relay already fitted then the easiest way to attach the new wires is with piggy-back spade connectors, and it is completely reversible. However I already have a relay fitted using piggy-backs on the hydraulic switch and I want to retain that, as well as my tell-tale so I can continue to keep an eye on power going to the brake lights. I didn't want 'nested' piggy-backs i.e. one on top of the other, so I decided to utilise the bullet connectors which are close by where the main, rear and gearbox harnesses join together, and bullets on the new wires. You need a green wire to pick up the fused ignition supply for one side of the switch, as well as the green/purple going to the brake lights from the other side of the switch. The latter is easy as by substituting a 4-way bullet connector for the existing 2-way between the main and rear harnesses you can connect to the green/purple. And the green wire is just as easy as there is one of those going from the main harness to the gearbox harness on all MGBs from March/April 1967 for the reversing light switch. If you don't have that then you will have to pick it up from the brake light switch.

    Supplementary brake lights: June 2021
    Third brake lights have been around a long time and while relatively easy to install to a GT behind the hatch they need to be slim to avoid obstructing the rear-view mirror. However roadsters are another matter needing some protuberance above the panel behind the boot lid, unlike OEM convertibles where it can be fared in to some part of the structure. Also possible on an MGB of course, but not as a simple add-on. But an MGOC forum post gave a link to something that combined high-intensity red lights with the white reversing light, which was worth investigating.

    Easier on the GT as it can sit behind the glass, and 'ready-made' are more likely to be suitable.

    Instrument Lights:

    Schematics:Up to 1969
      1970 and later
    Bulb Holders

    These are powered from the 'parking' or first position of the main lighting switch, and were never fused. Originally all cars had a rheostat between the speedo and the tach to progressively dim the lights including being able to turn them off altogether. Then North American MkII cars up to the 1970 model year had a simple on-off switch on the column shroud whilst other markets continued with the rheostat. In 1971 North American cars got the rheostat again and all cars continued with this until the end of production. This change for North America may have been due to lack of space on the first version of the padded dash. Until the 77 model year RHD cars always had the rheostat between the speedo and tach. LHD 'padded dash with glovebox' cars regained the rheostat on the right of the instruments between the choke and heater switch until the 77 model year. From 77 onwards RHD cars had it on the lower edge of the dash under the speedo. From 77 on LHD cars had the rheostat on the extreme left-hand side. 1977 and later models had the switches and heater controls illuminated at night as well as the instruments.

    From the rheostat or switch to the gauge lamps the wire colour was always red/white, picking up an earth from the instrument case. On two-fuse fusebox cars the wire from the main lighting switch to the rheostat or on/off switch is red, on 4-fuse fusebox cars it is red/green. My V8 rheostat exhibits a smooth change in resistance from almost zero ohms at the 'bright' end increasing to about 10 ohms just short of the 'dim' end, then goes fully open-circuit for the last bit of travel to fully extinguish the lamps. The roadster has the 'off' section at the bright end. Both were faulty when the cars came to me, I remember paying top-whack for the roadster one, but gibbed at that when I had to replace the V8 one as well so bought a cheaper version off eBay, which probably explains the 'reverse' operation.

    Bulb Holders:
    The original 4" speedo and tach use claw-type holders with a single wire for the 12v supply as they pick up an earth from the gauge body. The smaller 80mm speedo used on all V8s, and RHD RBs, and North American spec Mk2 (prior to 1977 at least) use a holder that pushes into a tube on the back of the gauge, and also only have one wire. The smaller fuel and dual gauges use the same tube-type fitting. My 73 and 75, and a 1980 that I rewired, all use MES E10 screw-fitting bulbs and holders. However a replacement harness for the 1980 came with T10 capless/wedge-type bulb holders. The problem with those in pre-77 gauges is that the bulbs can get dislodged and fall inside the gauge. The original tube-type holders for MES E10 bulbs don't seem to be available any more. T10 capless are available but have two terminals as the body is plastic and you have to make your own arrangements for earthing, as well as the problem of the bulbs falling in the gauges. A better alternative that is also available is the BA9 bayonet holder which picks up its earth from the tube the same as the original holder so only has a single terminal. These, and single-wire claw-type MES E10 holders are available from the likes of AES.

    The Parts Catalogue under 'toggle/rocker switches' lists rheostat BHA5047 but only for 360301 on i.e. rubber bumpers and all V8s. For LHD it lists BHA5198, replaced by 37H7994 with knob 37H7995. Current supply in the UK (for all years) is BHA4278 which seem to be wire-wound (instead of the printed-circuit type in previous cars as well as the ones Bee and Vee came with and their replacements) at typically £22 to £27 (October 2019, although some sources are higher), which is a lot cheaper than the £50-60 I was seeing just a couple of years ago. I jibbed at paying the higher price to replace Vee's from the usual suspects many years ago and got one elsewhere, but discovered it functions the other way round i.e. anti-clockwise for bright then off instead of how I remembered it before. No big deal, it's not something I ever use anyway, I just don't like things not to work.

    The rheostat knob is retained on the shaft by a push-button in the shaft which fits in a hole in the knob. The push-button must be depressed as the knob is withdrawn. The push-button is on a strong spring, and even when depressed the knob can be seized onto the shaft. The rheostat is usually retained in the dash by two nuts. The inner nut is to allow the threaded portion of the rheostat body only to protrude through the dash far enough to get the outer nut on for a neat appearance with no free threads showing. This picture shows a chrome nut, on the MGB it is usually a slotted ring which strictly needs a 'ring-driver' to remove and refit, but if used carefully long-nosed pliers or a screwdriver and light hammer used as a drift will suffice. When replacing the knob you should notice that one face of the hexagonal hole is spaced back more than the others, this must be placed over the push-button on the shaft, and depresses the push-button as you push the knob onto the shaft, until it clicks into place.

    On CB cars (except V8) there is a dashboard bracing panel behind the rheostat and between the main dials which means one of the main dials has to be taken out first in order to remove, or even access the terminals, of the rheostat. V8s and RB cars don't have that bracing panel and the main dials are smaller so the rheostat can be reached from behind more easily. Maybe tricky to juggle connections while fitted, but it's relatively easy to remove the knob, locking ring and wavy washer and pull the rheostat back and down for better access.

    All the rheostats I've had (several cars) have been of the printed circuit variety where the changing resistance is obtained by having printed circuit tracks of various thickness and length switched in and out as required. If all the instrument lights fail the rheostat is a likely cause. They are quite expensive for a) what they are and b) the use they are, even with uprated instrument lighting. Nevertheless I have always replaced mine as I hate things that don't work properly, and haven't had a subsequent failure, even on cars used as daily drivers with a lot of 'lights on' use particularly in the winter. As these lights are unfused it has occurred to me that maybe one of the lamps was shorted out at some time in each cars life, which would destroy a printed-circuit rheostat pretty-well instantly.

    If your panel lights are dimmer than you think they should be, or don't work at all, the first thing to do is try bypassing the rheostat to see what happens. Although the rheostat only has two connections (it is just a variable resistor) you will actually see four spades in a row. Each connection has two spades, bent into a 'U' shape and riveted to the body in the bottom of the 'U', and the two 'U's are side-by-side, with a bigger gap between the 'U's than between the two spades of one connection. All years of MGB have one red or red/green wire on the one connection leaving a spare spade. Some years only have one red/white on the other connection also leaving a spare spade, so it is a simple matter to move one wire from its connection to the spare spade of the other connection to bypass the rheostat. It doesn't matter which wire goes on which connection. Other years have two red/whites going to the rheostat, in some cases in one spade connector so you can bypass the rheostat in the same way, but it seems that some may have two separate wiring connectors which occupy both spades on the rheostat output connection, meaning you can't get both on the input connection (which would require three spades), but you can still transfer one of them over to bypass the rheostat for some of the lamps to see if that makes them brighter. If you want to bypass the rheostat permanently for all lamps on these cars then you will need a Y-connector like these. You could use a Scotchlok but it would mean cutting the connector off one of the wires and they aren't the most reliable of devices.

    If you have changed the instrument and control bulbs from the original filament-type to LEDs, the rheostat will no longer work as originally, as described here.


    Uprating Instrument Lights: 

    That leaves us with the normal situation of dim lights when everything is working as it should! It has often been said that the provision of a rheostat must have been a joke by someone in the factory, as with the best will in the world they are never going to be too bright with the standard bulbs. Incandescent bulbs do blacken on the inside as they age, failure seems very rare so most of them are probably very old, and replacement might help. Cleaning the inside of the cans and the back of the glass can help, as can repainting the inside of the cans with gloss white or silver, but is a bit of a fiddle and you could end up damaging the instrument. But is it even an issue, I ask myself? The beauty of analogue instruments is that you don't have to read the numbers anyway when you are familiar with the gauges, just be able to see the angle of the pointer. You don't read the numbers when you look at a clock or watch do you? You just look at the angle of the hands, and how many watches and clocks these days have numbers on them anyway? Over several years I tried a number of options, and whilst some were better than others, none were really worth the effort and/or cost.

     February 2013:
    But as time goes by and the years mount (mine), as well driving other cars and infrequent driving of either of the MGBs at night blunting familiarity with what the needle angles mean in particular the relationship between speedo needle angle and speed, improved brightness is probably becoming more necessary. Whilst investigating DRLs I had come across a 5-element LED which was worth trying in the gauges. It had a T10/wedge fitting for the rubber bumper pilot light in the headlights so not a direct replacement in the instruments on either car. But I had a wedge holder lying around and tried just holding it in position for the chrome bumper speedo and tach and it gave by far the best improvement of anything I had tried before. This is almost certainly due to the four radial elements being inside the case as well as the one forward facing. At the time I couldn't find any bulbs of this type with an MES (medium Edison screw, which is what all eight of my instrument bulbs are) fitting, but did find some bayonet types, so fiddled about quite a bit with wedge and bayonet holders and ended up with the speedo and tach on both cars much improved.

    The ancillary gauges (and the smaller V8 and rubber bumper tach and speedo) have 12mm tubes on the backs for cylindrical bulb holders. Two of the previously obtained screw-in LEDs worked well in the dual gauge, but in the fuel gauge whilst they changed the hue to a blue/white the same as the other gauges they were not really any brighter, and even these new 5-element bulbs (wedge and bayonet) held in place seemed no better. This is largely because the fuel gauge has a completely different light path to the other gauges.

    I was convinced there must be an MES i.e. standard screw fitting version of these bulbs, so kept looking from time to time. And while Googling '12v MES LED' I realised that an alternative description for the fitting was 'E10'. Googling that instead of MES got a couple of hits for the correct type of bulb, but it was factories touting for bulk purchases and wholesalers with bundles of 100 units. But then I noticed they all had the same description 'E10 5 5050 SMD LED' and Googling that led me to a pair for £2 and free shipping from China! A pal ordered a set, supposedly delivery in 30 days, but they actually took more like six weeks, with no response to emails, and while we were waiting there was a flurry of bad feedback complaining of non-delivery and no response to emails! Eventually they turned up after about six weeks. In the meantime I had found another source, also in China, just under £4 for a pair so nearly double the price but still very cheap. They only took a couple of weeks to arrive, so the extra cost is obviously to pay for a faster type of snail. And trying those with the standard holders does give a noticeable improvement in the fuel gauge on both cars! So both cars now have four legible instruments.

    The upshot is that these are a direct replacement for the standard tungsten bulbs and give a real improvement, so no fiddling around with alternative holders. And whilst they are a plug-in replacement for the 4" speedo and tach, the 80mm tach and the matching dual and fuel gauges, there may be a clearance issue with the 80mm speedo on the V8 and rubber bumper cars needing the holder to be spaced back a bit as I had to do with the BA9 versions. And I haven't tried these in any of the 77 and later plastic gauges. These have a green plastic bowl over the end of the standard bulb which will limit how far an alternative bulb will project into the instrument. It's also why you have to be careful with halogen bulbs, as being much hotter they can melt this green bowl.

    October 2021: The fuel gauge has seen the least improvement, but then in an MGOC forum post someone posted a link to a 'flat faced' unit with eight small elements all facing forwards instead of only one facing forwards and the rest distributed round the sides. That does give a small improvement to the fuel gauge to make it about the same as the dual gauge. But while Googling for those I spotted another type with one large yellow element covering the whole of the end of the 'bulb', and these were described as 'COB' instead of 'SMD. Googling that I discover that while SMD (Surface Mount Device) are packaged discrete LED units each with their own connections soldered to a substrate, COB are 'chip on board' which are bare LED chips directly in contact with a substrate to produce arrays. This allows for a much higher packing density and hence a higher number of lumens per square mm, for example giving nearly 10 times more elements in the same space compared to SMD, and nearly 40 times more than wire-ended leds. Some 1W on order, then I found some 2W so ordered those as well!

      However you will find the rheostat no longer works as it did. If you have all LED bulbs then really it won't dim them at all, if you have some tungsten bulbs left - i.e. in the cigar lighter or a clock or auxiliary instrument, then they will all dim slightly, the filament bulbs more than the LEDs. However the rheostat should still turn them off altogether as before. This is because the LEDs draw so little current, which means virtually no (no tungsten bulbs left) or very little (a couple of tungsten bulbs left) voltage is now being diverted to the rheostat so all or nearly all the voltage is still at the LEDs at the maximum dimming position. These 5050 SMDs take 30mA each whereas the original 2.2w filament bulbs take nearly 200mA each i.e. nearly six times the current. With an 8 ohm rheostat at full dimming there is only 7v left for four filament bulbs which are almost fully dimmed, whereas there is 11v for four LEDS, i.e. very nearly full voltage and very little dimming.

    I know of a couple of cases where someone has gone to quite a bit of trouble to attach a conventional potentiometer of a higher resistance value to the back of the rheostat control to retain originality on the dashboard, but this isn't really necessary. By adding a load equivalent to the replaced tungsten lamps you will restore the function of the rheostat to a large extent. For example if you have replaced four 2.2w tungsten bulbs with 5050 SMD LEDs you need to generate 8.8w of load for the rheostat to work something like normally. 5050 SMDs take 30mA each or 1.5w for four, so you would need 7.3w of load from a parallel resistor, which at 12v represents 20 ohms. 8w minimum dissipation, 10W and 20w are available from the likes of RS Components and Farnell. However due to the different voltage/illumination characteristics of LEDs and incandescent the dimming may still not be exactly the same. A more sophisticated alternative would be to use the standard rheostat to control a transistor to give the required range of voltage output, and that is the next project.

    Herb Adler has done a similar thing, see the appropriate section in this edition of his sagas.

    September 2020: While browsing the Classic Car LEDs website I came across the following statement:

    Do LEDs work with Dimmers?

    A very common Classic Car owner question. Briefly, ours do with the old style internal variable resistor in the dimmer. This reduces the voltage available to the LED which in turn reduces the brightness. LEDs are far more sensitive than incandescent bulbs though which means a small change in the dimmer will have a bigger effect.

    That's absolute nonsense as anyone who has converted to LEDs will know. I politely advised them of mine and others experiences, and they wrote back: Regarding dimming of the dash LEDs, whilst ours will dim, it will depend on the condition and voltage range of the rheostat. The LEDs will dim faster than an incandescent and have a working voltage range of 9-15 volts. Below 9 volts they nearly extinguish so a lot will depend on the range of your rheostat. Which may well be correct but ignores the fact that with LEDs the current through the rheostat is far less so the voltage drop across it is less, leaving more for the LEDs on full dimming - 11v as described above. I pointed out that vendors of LEDs for indicators often say you have to fit load resistors to take more current and make the flasher unit work properly, and they wrote back "11 volts is near full brightness with the LEDs so a resistor would help."! Yes it would, knocking the argument about less current into a cocked hat, and ignoring their original incorrect statement. At which point I left it there as we had gone full-circle. I'm increasingly finding these days that more and more people are incapable of holding more than one stage of a discussion at a time in their brains. Step forwards twice in the discussion and they have forgotten the original point that was being discussed. Even when it is written down in a forum thread. Bloody annoying, as is when they blame an incomprehensible post on the 'spell checker', when it's predictive text and not a spell checker, and it's because they didn't read what that had 'written' before they clicked Send! Rant over.

    Fusing: October 2019

    • Headlights and instrument/switch lighting were never fused from the factory.
    • Factory or dealer-fitted optional front fog and spot lights or rear fog (1980) were never fused from the factory.
    • The headlamp flasher circuit (optional and factory) was initially unfused and powered from the brown circuit, changing to the purple fused (always live) circuit for North American on Mk2 cars, but not until 1970 for other models.
    • Brake lights and indicators were always from the green circuit in the fusebox until 1978, then from an auxiliary green circuit fed by an in-line fuse under the fusebox.
    • Parking and number-plate lights were unfused on Mk1 cars, on Mk2 cars prior to 1970 with the two-fuse fusebox there were two in-line fuses by the fusebox one feeding the front and the other the rear, and from 1970-on there was a four-fuse fusebox with the top two fuses feeding the corners of the car, one for each side.
    • The map light was always unfused off the parking light circuit.
    • Factory-fitted reversing lights (March/April 67-on) were fused from the green fuse in the fusebox.
    • Courtesy and boot/load space lights - optional and factory for Mk2-on - were always powered from the purple fused circuit.
    • North American side-marker lights powered from the headlight circuit prior to the seat-belt warning system fitted during 1972 were unfused. After that when powered from the parking light circuit they were fused with the parking lights.
    Any unfused circuit can cause severe damage if the wiring should short out. Note that on cars with the main lighting switch in the steering column shroud it is easy to trap the switch wires against the column when refitting the shroud. Eventually the plastic insulation will fail and cause a short circuit, which will cause considerable local damage. And if it is the brown wire that affected while the car is unattended, could result in a fire. Care also needs to be taken on Mk2 North American spec prior to 1971 that have a simple on/off switch for the panel lights on the column shroud, in place of a rheostat on the dash.

    Particularly when fitting relays to the headlight circuit consideration should be given to adding fuses as the greater current that relays will allow to flow will cause more damage and faster. It is advisable to add one fuse per filament if you are not to be plunged completely into darkness from a fault at one headlight, more information here.

    Parking light circuits on Mk1 cars can be fused as per early Mk2 cars i.e. one fuse for the front and another for the rear, inserted where the two red wires in the main harness (12v supply and feed to front lights) and the red in the rear harness come together. Part the three wires and determine which from the main harness carries 12v with the lights turned on, and connect that to a 4-way bullet connector. Connect two in-line fuses to the other side of that, one going to the other main harness wire via a 2-way bullet connector, and the other going to the rear harness via another 2-way bullet connector.

    Instrument/switch lighting circuits have been known to cause wiring damage, and on every car that has come to me with rheostat lighting the rheostat has been burnt out, possibly from previous shorts by the instruments, and fusing these depends on the year of the car. To add a fuse ideally it should be as close to the main lighting switch as possible, where the red (prior to 1970) or red/green (1970 and later) wires have two branches one to the parking lights and the other to the instruments. On 1977 and later this will be where the lighting switch sub-harness plugs into the main harness with a multi-way plug. However this does mean guessing which one of the two wires to cut, and you have a 50% chance of getting it wrong.

    On Mk1 cars the parking lights weren't fused either, so an in-line fuse with a female spade one side and a male the other between the two red wires and the lighting switch will protect all of them ... with the proviso that a fault at the instruments will extinguish all the rear lights. Mk2 cars prior to 1970 still had the two-fuse fusebox, but had two in-lines in the parking light circuits one feeding the rear (which again would extinguish all lights at the rear if it blew) and the other the front, where at least you have headlights.

    The alternative is to insert it in the red/green at the rheostat using an in-line fuse with a female spade one side and a male the other, but even that is complicated prior to 1971 because as well as the red/green feed at the rheostat there is a second wire daisy-chained on to the map light. In that case inserting an in-line between the two red/greens and the rheostat would protect the instrument lights, but not the map light.

    Factory/dealer/PO-fitted fog and spot lights should be easy to fuse where the switch supplies are picked up from existing parking and headlight circuits.

    For unfused headlamp flasher circuits it should be possible to add an in-line fuse at a bullet connector behind the dash where the tail from the indicator/flasher switch connects to the main harness. However the diagram for 62 to 64 cars shows the brown wire going all the way back to the fusebox. If this is a single wire in a spade connector it can simply by moved to the other end of the same fuse i.e. the purple circuit to fuse it.

    For North American side marker lights powered from the headlights there are three blue wires joined together by the fusebox - two from the main harness one of which is the 12v supply the other going to the front markers, and one to the rear harness for the rear markers. Identifying which of the two blues from the main harness is the supply, and inserting an in-line between that and the other two blue wires will protect both front and rear marker lights.

    The factory-fitted rear fog light circuit almost certainly uses multi-way plugs and sockets to connect the manual switch to the headlamp circuit i.e. no bullets or spades, so a blue wire would have to be cut to insert a fuse. As there are two blue wires at the main lighting switch and you have a 50% chance of getting it wrong, it makes more sense to cut the single blue at the manual switch.

    Switch Illumination: June 2013

    For the 77 model year on the factory supplied night-time illumination of the switches and heater controls from an internal bulb in each, but on earlier cars you have to grope in the dark to some extent.

    About the same time Michael and I were fiddling with the instrument lighting we had the idea of using LED strip to illuminate the dash, particularly the switches. 77 and later MGB have illuminated switches and heater controls so are already catered for. Available in a variety of colours, we decided to be relatively sober and act our age choosing warm white over other offerings such as blue, green, red and yellow.

    The strips can be cut to the required number of LED elements, where there are typically four short copper strips between each group of three LED elements, three elements being the minimum that can be powered off 12v without an external resistor (but see below). Unless you are going to daisy-chain two or more strips, cut to the end of the strips rather than in the middle, and that gives you more copper strip to make a connection at one end, and none at the other.

    There are connector blocks available but they are relatively big, the type to connect two strips are relatively cheap but the end ones with wires are four times the price. You can use the first type with wires, inserting the strip into one half and the wires into the other, but it's just as easy and makes a perfectly good connection by soldering direct to the copper strips, then using heat-shrink to cover the connections, and a blob of silicone sealant in the open end to stabilise the wires. The copper strips are very close to one of the elements so it's preferable to use enough heat-sink to cover the nearest one and so get a stronger joint.

    Mounting them under the dash crash pad makes them unobtrusive if not invisible from the driving seat, and the wires can be fed through the gap between the top of the dash proper and the dash top under the crash rail. Depending on how the dash and crash pad have been fitted there will either be a clearly visible gap to feed the wires through, or you may need to wiggle a small screwdriver through to open this up.

    Although the LED strips are self-adhesive and have a peel-off strip the textured surface of the crash pad will limit its effectiveness so you will probably need to use an additional adhesive, such as Copydex, or silicone sealant.

    The LED elements are quite bright and so you may need to use a series resistor to bring this down to an acceptable level.

    Michael used 330 ohms in series with nine (one concealed) 5050 elements, I used 1.5k although anything from 1k to 1.5k gave very similar results. Herb Adler used 1.8k ohms in series with six although I don't know whether his are 5050 elements or not. Each group of three are effectively in parallel with all the other groups of three across the voltage supply, so the more groups of three you use the more current they will draw. This means theoretically the resistor to achieve a given brightness will vary according to how many groups of three you have used, i.e. a lower value for more groups, but in practice they take such a small current that choice of resistor is going to be down to personal preference of resultant brightness rather than how long the strip is. A resistor, if fitted at the end of the wire where it joins the white/red instrument lighting feed elsewhere, also means that the current will always be at a safe value even if the wiring or LED strip should happen to short out. For example even 330 ohms will limit the current to 42 milli-amps, whereas a single 2.2w instrument bulb takes 160mA.

    A shorter strip can be fitted below the dash to illuminate the centre console. Join the wires from the two strips together, via a single resistor, to the instrument lighting feed.

    Reversing Lights:

    Reversing lights with auxiliary brake light function

    Factory equipment from April/May 1967, may have been a factory fitted option before then. The lens screws through the body of the light unit into captive nuts behind the rear panel, and unusually there is a 2-'pin' plug on the harness that connects to two small spades under the light unit. The bulb is a festoon-type GLB270 (18W, North America) or GLB273 (21W, elsewhere) although these days some describe the GLB270 as '18/21W'. There are several different lengths of festoon and these are 44mm. The lens (37H1760 with gasket 37H1759 and two screws 37H3751) seems to have a silvered coating on the back round the edge as a pseudo chrome bezel. The light unit complete with lens is BHA5167 and also uses gasket 37H1759 to the body.

    The reverse light switch is screwed into the upper half of the gearbox and can be seen on the right-hand side looking directly up into the narrower part of the tunnel. Access to this switch is not easy, but disconnecting the rear cross-member at the chassis rails allows the gearbox to swing down a little for better access. You can also remove the centre arm-rest/cubby (where fitted) and pull back the tunnel carpet for some access from above. On 3-synch cars there is a large access panel on top of the tunnel that can be removed, but even on 4-synch cars there is a small panel in front of the gear lever which can help. Note that OD gearboxes prior to September 66 may not have provision for a switch, unlike early non-OD gearboxes.

    The only 'adjustment' on these switches is provided by spacers, and a loose or worn switch can prevent the light coming on or make it erratic. In the case of wear causing non or erratic operation removing a spacer may be all that is required. OTOH a missing spacer can cause it to be on when it shouldn't be. It's always been said that these spacers are fibre, and there were originally two of them. However on Vee the OD switch spacer is copper and the Parts Catalogue only shows one per switch. Various suppliers only indicate one (1B 3664), and fibre, but Brown & Gammons shows a fibre washer for the reverse switch and a copper for the OD (3H 550), which is the same as for the brake banjo! Incidentally the OD and reverse light switches are the same part number. Vee's reverse light switch has one thin fibre spacer so exactly as per Brown & Gammons, and this is noticeably thinner than the OD copper spacer.

    Automatic Gearbox:
    The automatic gearbox uses a completely different switch that combines the reversing lights and inhibitor functions. It screws into the side of the gearbox and there is a calibration process to ensure it is screwed in to the correct position.

    Map/Interior Lights:

    Door switches

    Map Light:

    Originally the MGB had a map light for the passenger, controlled by an on/off switch close by when the main lighting switch was in either of its 'on' positions. On Mk2 North American cars the map light moved to a centre console, replaced by a courtesy light in 1971. For 1971 only non-North American cars had the map light available at any time with the on/off switch, as well as being lit from both driver and passenger door switches, in 1972 it was replaced by a central courtesy light. Map lights were never fused.

    This light (when fitted to the dash i.e. excluding North American centrally mounted lights) is a little confusing as many parts sources indicate it is the same as the number plate light that attaches to the overrider, but this is only partly the case: It uses the chrome cover (37H5426), glass dome (606078) and seal (17H5302, this should be a round seal but some suppliers have it as a diamond-shaped seal which can be cut down) from the number plate light. However it doesn't use the bulb holder, and it is a little cheaper to get the individual parts. For the bulb holder it uses a claw-type holder with a 2.2w bulb the same type as for the speedo and tach. Well I say the same type, and whilst the UK diagrams do show what would appear to be a one-wire bulb holder which picks up an earth from being clipped into the dash (confirmed by Bob Gibbons with his 1964 LHD), a replacement harness has a red/green and a black wire going to a 2-wire claw-type bulb holder, so has a wired earth. This is preferable as a freshly painted dash may not supply a decent earth without scraping some of your precious paint off, but does not appear to be listed separately in the Parts Catalogue. Indeed it doesn't appear to be listed by any of the usual suspects, although I did find a 2-wire claw-type holder listed under part number AEU1313 from a number of non-MG sources. North American spec schematics for Mk2 cars do show a wired earth.

    The red/green from the bulb holder goes into the harness and back out again with a red wire from the main lighting switch. These wires have spades on a replacement harness (as does Bob Gibbons' 1964 LHD), but current stock from UK suppliers shows the switch as having screw terminals.

    Courtesy Light:

    From the Leyland circuit diagrams North American Mk2 cars seem to have had a central console with a map light controlled by a separate rocker switch, and an optional courtesy light with a manual switch as well as being operated by both doors. However Clausager indicates they had the map light until 1970, then from 1971 the courtesy light. The following year i.e. 1972 non-North American cars had the map light replaced by a central courtesy light, lit from an integral manual switch as well as from driver and passenger door switches at any time. But again the Leyland circuit diagrams are confusing in that they show an optional interior light controlled by two door switches in addition to the map light, from 1968 to 1970. Again Clausager indicates a simple change from one to the other for the 1972 model year, when non-North American cars gained the centre console.

    Note: Haynes issue dated 2010 with coloured schematics has an error in the drawing of the courtesy light for 1973 cars, and later. As shown it wouldn't work at all from either the door switches or the manual switch, but if both are operated at the same it will blow the purple circuit fuse. Earlier versions e.g. my 1989 copy are drawn correctly.

    Getting to the bullet connectors behind the console for the courtesy light, lighter socket etc. is a real pain as there is not enough slack in the harness, so I made an extender.

      October 2017: Since getting Vee back on the road I'd noticed that unless the passenger door was fully shut the courtesy light wouldn't go off. I didn't do anything about it as if anything it acted as a safety feature warning that the door wasn't fully shut, like modern cars where the switch is on the B-post. But I wasn't totally happy with the alignment of the passenger door, so slackened the door to hinge screws, lifted the door very slightly and retightened. That put the door right, but also means the light now goes off when the door is only half latched, as it always used to before. I mentioned this in connection with an MGOC thread on door hinges, and John Holland said he had to add a packing piece before his would go off at all. Given the amount of travel of the switch plunger after the contacts open I'm amazed they are so marginal.

      LED upgrade:

    On a trip away I must have caught Vee's load-space light switch and knocked it on when getting bags out, but wasn't made aware of it until some 30 hours later. Fortunately she still started, but it got me thinking about LED replacements for the interior lights in case it happened again, as well as for their increased brightness. LED replacements for the GLB254 6w festoon are commonly available, but I came across two types. The one with three 5050 SMD elements and a resistor seem to be the most common at around £2.50, but I also found one with two tiny elements and additional electronics, and an alloy heat-sink at £1.50. Now one would expect the first type to be better, but I was intrigued enough (and the cost was low enough) to buy one of each.

    Testing them the Cree-type was obviously much brighter, but how to compare them in a photograph without a lot of fiddling around with wires and holders? I put them in the reversing lights! One thing to note is that the 3-element type are polarity sensitive so if they don't work one way round try them the other. The other type are not polarity sensitive so work either way round. The 5050-type are really not much brighter that the originals, only whiter, which seems to be the case for stop/tail LEDs at least. It will be good enough for the V8 load space, and I'll use the Cree-type for the interior light. The supplier had one remaining Cree-type so I ordered that as well for Bee's interior light. She already has an 'eagle-eye' LED boot light which is a great improvement over the standard light.

    The Cree-type are so bright that I was tempted to buy more for the reversing lights. The supplier had no more, and whilst they are available elsewhere they are typically £6 each or two for £8, or I could settle for the less bright type. But there is also the issue of legality and acceptability to insurance companies, and having read of someone with LED number plate lights having an insurance claim refused I decided to leave them as they are.

    That leaves the current drawn by each type:

    • The original 6W festoon takes 350mA
    • The 5050-type LED takes 28mA
    • The Cree-type LED takes 225mA
    • And out of interest the single Eagle Eye in Bee's boot takes 50mA
    So whilst the 5050 type takes less than 10% of the current of the originals giving a big reduction in load, the Cree takes about 70% of the original. So a small reduction in current but a huge boost in output - horses for courses.

    I've used 'Eagle Eye' LEDs for DRLs and they are very effective. I've also used one in a trial of a vastly improved boot light, and it occurs to me that they could be used as 'puddle lights' when mounted in the bottom of the door, and red versions as rear-facing marker lights as the doors are opened. However these last two would require the drilling of holes in the door case.

     Door switches Added October 2011:

    BL door switches (always BHA4593 for the courtesy light) were always subject to water ingress and corrosion as they are effectively outside the cabin, giving flickering of the courtesy light or failing to operate at all. Two of mine were like that so I replaced them, but at the time the original style were not available and the replacements were not only different in appearance but also needed the hole in the A-post opening up a little bit. By 2012 Brown & Gammons (and others) have the correct switches, but dodgy switches may be recoverable, particularly if they are only intermittent and not so badly corroded they don't work at all or have crumbled away, click on the thumbnail. This should only be a problem for the main doors, the roadster boot lid and GT hatch seals should be protecting those switches completely.

    Note that North American spec cars from 1970 had a 'key in, door open' warning buzzer that involved a second switch BHA4984 on the driver's door. This switch has two wires and both contacts are insulated from the body i.e. is totally different to the courtesy light switch, so problems and possible fixes are probably different as well.

    Boot Light:

    Both UK and North American roadsters had a boot light (BHA5040) from the 1971 model year onwards, fused from the purple circuit, operated by a switch (13H391) activated by opening the boot lid. These switches are inside the boot so protected from weather.

    However whilst the light gives a reasonable light when there is not much in the boot, if it is fully loaded it gives virtually no light at all. A pal had the idea of using one of the 'Eagle Eye' LEDs I had used for the DRLs, and it works very well. Tucked up into the recess of the boot lid reinforcing frame where the latch release button is, but positioned to one side so it doesn't interfere with the mechanism in either the locked or the unlocked positions, it is at the perfect angle to illuminate the whole of the boot with a bright white light.

    GT load-space light:

    Both UK and North American GTs had a load-space light (EAM1651) from the 1971 model year onwards, fused from the purple circuit, with the switch (13H2018) operated by the hatch being opened as well as a manual switch, and again the switches are inside the cabin so protected from weather. Not sure why it needs a manual switch ... unless someone is sitting (never 'sat'!) in the back ... reading a magazine ... in the dark.

    While updating the courtesy lights with LEDs I took the opportunity to do the same with the load space, and replace the melted cover.


    North American side marker lights:

    Side marker lights appeared in the 1970 model year and were powered from the unfused (it is easy to fuse them) blue circuit to come on with the headlights - dip or main. In 1972 cars with the sequential seat belt system and later, each unit is wired to the nearest side/tail light assembly and hence comes on and is fused with them from the top two fuses in the four-way fuse block. Side-marker lights always had a wired earth, shared with the headlights at the front and the reversing lights at the rear.

    Fog & Spot lights:

    Auxiliary switches


    The optional factory-fitted front spot/driving lights were always wired to be available with the main beam if required. From inception until 1970 optional factory-fitted front fog lights were wired, via a switch, to be available with the side lights if required. Factory or dealer wired fog and spot lights were powered from unfused circuits, but it should be easy to add fuses.


    From the 1970 model year the front fog lights were wired to be available with the dipped beam if required, maybe a regulation change, but this renders them pretty useless as dipped beams throw back a lot of glare in fog. By the time my 2004 ZS was built regulations allowed front fogs to be available with the parking/position lights on only.


    A pair of square Lucas rear fog lights were factory-fitted to all home-market cars for the 1980 model year, wired to be available when the headlights were on dipped or main beam. Again, if driving in thick fog with front fogs on without dipped headlights this means rear fogs wouldn't be available. This time my ZS is the same - if only the rears are turned on, but if one turns the front fogs on with parking lights then the rear fogs become available - sensible.


    You have a number of options as to how to wire them - available all the time; available when the side lights are on; or available when the appropriate headlights are on. In all cases except the first a relay should be employed to reduce the load of the extra lamps on existing wiring and switches to a minimum. All additional lamps should employ an in-line fuse, which if standard-gauge wiring, switches and relays are used, can be a standard 17-amp rated, 35-amp blow fuse. A lower-rated fuse could be used, but why complicate matters with a proliferation of fuses with different ratings? And if an auxiliary lamp fuse does blow it can be replaced with one of the spares from the main fuse block - once the fault has been cleared of course. I suggest that a single fuse for all lights is adequate except for night rallying when separate fusing of each front light, including each headlight filament, would be more robust.

    Personally, I have my front and rear fog lights wired so that they are available when the side lights are on as I can't see much point in having front fog lights if you can't use them without being dazzled by the glare thrown back by normal dipped lights. The following schematic has all three types of lamp wired in this way:

    My 2004 ZS is wired this way from the factory, although I'm told by people from North America that this is illegal there and they can only be used with headlights. I have a vague recollection that the UK might have been the same some time ago, if so common sense has obviously prevailed since then. The MOT requirement is: "Front and rear fog lamps are permitted to operate independently of any other lamps or ignition systems." (MOT Manual Section 4.5.1). A 'tell-tale' indicator is required but only for mandatory rear fog lights i.e. on vehicles first used after 1980. At one time the manual said it could just be a coloured tag visible when the switch is operated as well as a light, but now it mentions neither (MOT Manual Section 4.9). I.e. it could be either, but it will only be checked for mandatory lights which from the factory did have a light.

    Rectangular fog (kerb-side) and spot lights as fitted to my V8. However as the glass on the spot got broken many years ago, and I haven't needed to use the fog light for even longer, after the restoration in 2017 I didn't bother refitting them.

    People sometimes suggest using the off-side reversing light as a rear fog light with either a red LED or red lens fitted. The Road Vehicles Lighting Regulations 1989 Schedule 11 2.(d) says that optional rear fog lamps must have a minimum separation distance of 100mm between a rear fog lamp and a stop lamp. On an MGB there is only 45mm between the illuminated reversing light and stop/tail lenses at their closest point which appears to preclude that. But Dave Birkby wrote on the MGOC MGB Technical Forum in April 2019:

    Before you go too far this modification would require informing the insurance company. Take the lenses of both the offside reverse and rear position/brake/indicator light unit off (the light emitting surfaces). Measure the distance between the reverse bulb and the brake light bulb to ensure there is 100mm separation, if there isn’t 100mm they would not approve as it contravenes the Road Vehicles lighting Regulations. And in a subsequent post emphasising: But, it is the bulbs and not the lenses, and the glass section of a festoon at that. That is how moderns get through type approval if they are combined in a lamp. More recently (November 2020) the question was asked again, I posted the above, and Richard Massey quoted the IVA which shows the distance as being measured between the lenses. But Dave also wrote in April 2019 about when fog lights are permitted to be shown: That is the law for cars that have been type approved or had to go through IVA. Our cars have not had that process so they do not need to comply. IVA is much stricter than MOT, but they are different tests. The upshot is that the MOT checks neither distance not light source, but an external LED may cause problems in an insurance claim. Staying with incandescent is probably not an option as they are 21W and get pretty hot. OK for the short period of use a 21W reversing light gets, but it would almost certainly damage the lens if used as a rear fog light.

    Front or rear fog lights can only be used in poor visibility e.g. fog, falling snow or heavy spray. If someone is travelling behind you in convoy, turn your rear fogs off, so they can better see your brake lights and not be dazzled. Never use them as a matter of course at night, particularly in built-up areas in the rain, the resulting dazzle for following drivers even travelling at a safe distance behind you severely limits their ability to see anything other than your fog lights - including your own stop-lights. In the UK it is an offence (Highway Code Rule 236) to use fog or spot lights inappropriately, you risk a £1000 fine - per light! Day-time running lights are different - they should come on when the engine is started, but must go off (or be dimmed) as soon as sidelights or headlights are turned on.

    Auxiliary switches:

    Fitted where you will, but on the V8 a PO had butchered the dash panel below the air vents to fit a mish-mash of switches for cooling fan override, front fogs, and maybe something else, which looked a mess. I was fortunate to get a set of three illuminated rockers comprising one with a fan symbol (which shows me when the thermo switch has come on as well as being able to turn the fans on manually), a red one (rear fogs) and a green one (front fogs) at Stoneleigh one year. Slightly bigger than standard, but with a fascia cover-panel cut from a piece of textured black plastic they cover the bodging pretty well. These illuminated switches have probably every logo variation you are likely to need, and whilst they are a more modern design of rocker they are said to be the same size as the MGB pre-77 rockers.

    Number Plate lights: April 2009


    Number plate illumination lamps were originally mounted on the rear bumper overriders (amazingly front overriders on UK cars were optional to begin with!). For the 1970 model year North American cars had two 'quarter' bumpers instead of a full-width and the lights were tucked inside the ends of these. They moved to the bumper itself for 1974 non-North American cars, to the number-plate backing-plate for North American 1974 model year cars with the 'Sabrina' overriders, and for all rubber-bumper models. When mounted on the backing-plate they had 12v and earth wires, but for the overrider and bumper-mounted types there is only a single wire to provide 12v for illumination and a very tortuous path for the earth return relying on the physical contacts between bulb, bulb holder, light unit, light unit plinth, overrider and overrider bolt (or bumper), bumper irons and body plus various nuts, screws, washers and bolts! Mine didn't work after restoration so I provided an earth wire from the light units back to one of the existing earth wires. lights.

    It was only when I received an email from Felix Weschitz in Austria saying he had the same problem, and couldn't find my own well-hidden comment on the problem, that I decided to add this specific paragraph, and a link to Felix's information. Reversing lights have an earth but that goes directly back to a number plate bolt on RHD cars so you will still have to do as Felix did, but cars for North America with side markers use bullet connectors for both those and the reversing lights so you can tap into those. Number plate lights mounted on the number plate backing plate (North American split bumper and all rubber bumper) were provided with earth wires from the factory.

    May 2017: Neil Harrison on the MGOC forum raised this problem, and a couple of us suggested the earthing. I mentioned I had run an earth wire in from a light-unit stud where it is inside the overrider. However he tried that, and it made no difference. So he dismantled the light unit and found it had been assembled such that the rubber gasket was completely insulating the bulb holder from the remainder of the fitting. Assembled correctly it worked and didn't need the earth wire. So if you have the same problem before going to the trouble of making up and installing an earth wire, clip a temporary earth to the light-unit stud inside the overrider, and see if that makes it work. If it does, then it does need an earth wire.

      Sheared stud repair: October 2016 When removing the light units from Vee's number-plate backing as part of her restoration I was annoyed to shear a stud on one of the units as otherwise they are both in as-new condition. Looking at the studs they have a shallow round head, then a short square shank, which is pressed into a square hole in the base-plate. "I can make one of those", I thought.

    I pressed out the sheared stud in a vice using a socket over the head. I found a cheese-head screw that fitted the other nut, and a nut that fitted the screw. I then filed the lower half of the head down into a square using a needle file. On the base-plate I used the square tang of a file in the square hole to bow it downwards a little, opening it out so the screw just fitted. Then using the 1/4" drive end of a socket, which just fitted over the square shank on the new 'stud', and a vice, pressed the base-plate round the screw flat again, so reducing the size of the hole, and pinching-up the screw. About an hour's work, and £20 saved.

    North American 'Key In' Warning June 2013

    For the 1970 model year North American gained a warning buzzer that sounded whenever the drivers door opened if the key was still in the ignition. This used an additional contact on the ignition switch to send an earth to the buzzer when the key was in, and an additional drivers door switch. This door switch (BHA4984) differs from the courtesy light switches in that it is insulated from the body and has two wires - a purple (always on, fused) supplying 12v to the switch and a purple/green going to the buzzer. Both switches have to be 'closed' to sound the buzzer, i.e. either the door being closed, or the key being out, will stop it. It stayed the same for the 1971 model year and the first four months of the 1972 model year, but when these cars got the seat-belt warning system in December 1971 it was combined with that.

    The ignition switch contact. Examination indicates that this contact is only closed with the key inserted and the switch in the 'OFF' position. However one would have expected it to also be closed in the 'ACCESSORIES' position, if not in the 'RUN' position as well in case the engine has stalled with the ignition still on. The Leyland Workshop Manual has a test procedure for the sequential seatbelt system including this warning feature, however it does not give different conditions for any of the possible ignition switch positions. Furthermore it says "Test 10 Warning buzzer: Requirements: (l) Warning buzzer operates - ignition key removed: Remarks: If the warning buzzer does not operate in (l), either the warning buzzer or the circuit wiring is faulty". This seems to be incorrect, as the warning buzzer should NOT operate when the key is removed, only when it is inserted, and the driver's door should be open as well. The Austin MG Technical Service Bulletin gives even less information, just saying "Connect wire (between) pins 5 and 7, Warning buzzer on" without saying anything about the ignition key or switch or drivers door.

    June 2020:
    Arthur Taylor writes that he has been working on two 1973 models where the warning buzzer sounds when the key has been removed but the steering is not yet locked. Looking at the Parts Catalogue and Clausager there were three different ignition switches for the USA, Canada, Sweden and Germany 1973 model year - at the start in September 72 and chassis number 296000, chassis numbers 324942 and 325855, and it changed again at the start of the 74 model year at chassis number 328800.


    What polarity is my car!?
    Which battery terminal is which?
    Polarity Conversion
    Dynamo polarity
    Coil polarity
    Tachometer polarity
    Fuel pump polarity
    Heater fan motor polarity
    Instrument stabiliser polarity

      First, a history lesson: Why was the MGB positive earth to begin with, and why are some even older cars negative earth? Originally negative earth was the norm as on the low-output HT systems of the day a positive HT pulse gave a better spark at the plug than a negative one. Wired negative return was also originally used, but it was soon realised that chassis return was cheaper and easier. Before plastic-insulated wire all sorts of other materials were used, but all had a certain amount of leakage where they touched metal parts, which were now at earth potential. It was then discovered that the leakage from wires at positive potential to the chassis at negative potential was causing the wires to corrode and fail, hence the change to positive earth. Battery terminals also suffer from corrosion, particularly with the proximity of acid, and it was found that positive earth reduced this as well. This now meant that any leakage caused corrosion at that point on the chassis, which wasn't ideal, but the chassis is a lot more substantial than the wiring. By this time modern coil design meant a positive HT pulse could be produced from a negative supply, so the spark wasn't adversely affected by the change in polarity. Post WW2 most wiring was plastic insulated, which has negligible to zero leakage, so the polarity issue went away. No point in changing back to negative earth just for that, but with the advent of television post-war, interference from the ignition systems of passing cars became an issue, and negative-earth system are easier to suppress. Nevertheless, the MGB and presumably other marques and models in the BMC stable, didn't switch back until the fitting of alternators in 1968, but certainly had adequate suppression systems before that. Electronic components in cars - transistor radios being the first - can be instantly destroyed by the wrong polarity, unlike simple electric components like bulbs and coils. Early radios usually had a polarity switch on the back, but with the growing use of electronics it was decided that polarity switches on everything would be costly, so a standard polarity need to be adopted by all manufacturers, and negative earth - for its suppression benefits - it was.

    Whilst there is no safety benefit with one polarity over another, whichever polarity you have it is very important to observe the same rule when disconnecting or reconnecting the battery, and that is to remove the earth connection from the battery first, and reconnect it last. This is regardless of whether the car is negative earth/ground or positive earth/ground, and the reason for this is that if your spanner should happen to touch the body whilst it is also touching the earth/ground post of the battery nothing will happen. Once the earth/ground connection is removed it is now safe to undo the 12v (aka 'hot' or 'live') connection, because if your spanner should happen to touch the body while it is on the hot post still nothing will happen because the earth/ground connection has already been removed. If you work on the 12v post with the earth still connected, and your spanner should happen to touch the body which on the MGB with its batteries in a hole in the rear shelf is very easy to do. This has the effect of shorting out the battery, generating a large arc which could cause any battery gases in the locality to explode, which can itself cause the battery to explode, and your face is quite likely to be right above it. Modern automotive advice sources often say to remove the negative cable first, but they are talking about modern cars which are all negative earth, and are not taking into account the many classic and older cars that are still positive earth. It's earth cable off first and on last, regardless of polarity.

    What Polarity is my Car!? July 2014

    Someone recently bought a 1965 MGB which came without a battery i.e. was a non-runner, and as these were originally positive earth, but many have been converted to negative earth, he was quite rightly concerned as to which way round he should connect the battery.

    The first thing to say is that if it has an alternator it has almost certainly been converted to negative earth, and very probably so if it contains any after-market electronic equipment like electronic ignition or a modern radio. Period radios often had a polarity changing connector, so this can be a clue. If it has a dynamo then it could be either polarity, according to which way it has been polarised.

    Another possible way to determine polarity is to examine the battery connectors. Are these marked + and -? If not, then on UK batteries at least, the +ve and -ve posts on the batteries are different sizes, and the connectors are similarly different sizes. The posts typically measure 0.756" for the positive and 0.690 for the negative, i.e. the positive is bigger. Try connecting them one at a time and see if that indicates anything by one way fitting better than the other. The original cup-type connectors will be obvious, but bear in mind that the bolt-up type can be bodged to fit either post.

    If it's a 62 to 64 i.e. with a mechanical rev counter instead of a tachometer, and if there is no aftermarket electronic equipment, then with one exception connecting the battery either way round won't hurt anything. The exception is fuel pumps. The original pump was capacitor quenched and can be used on either polarity. Later pumps were diode-resistor and are polarity sensitive. Connecting these the wrong way round still won't do any harm, but will cause the pump to take about 1 amp more current than normal. Later versions still have transient voltage suppression devices which again are polarity independent. You may have to take the end-cap off the pump to see if it has the diode-resistor, and if so which way round it is connected. However bear in mind that someone could have fitted a positive earth pump, then someone else reversed the polarity. Or indeed someone simply fitted the wrong type!

    As a 65 to 67 Mk1 (Mk2 cars were negative earth from the factory) it should have the electronic tach, which is polarity sensitive. I'm not aware of reverse connection blowing these up, but can't promise. Tachometers were marked with the original polarity - positive and negative - from inception, at least until they changed from chrome bezels to plastic for the 1977 model year. But bear in mind that a PO may have changed the internal wiring of a positive earth tach and not changed the legend on the dial. Short of removing that and opening it up and working out whether it has been modified or not, really you need to remove the white 12v supply wire from the spade connection on the back to protect the electronics while you work out what the polarity actually is. But it's complicated by having three white wires, the other two being the ignition feed, usually as a single loop of white going through the external pickup. And even if you do open up the tach, there is nothing to say that it is the original tach and was working before the car came to you.

    I would not recommend simply firing it up and seeing what happens to the battery voltage i.e. to see if the dynamo is charging or not. The dynamo will generate it's output voltage according to its polarisation, independently of the battery voltage. If the polarity of one is opposite to the other and the control box cut-out relay operates the voltages will be added together and a very high current will flow. This could well burn wiring and damage the dynamo and control box. Disconnect the wiring from the F and D terminals of the dynamo. Connect the battery using your best guess as to polarity, switch on, and start up. Then with the engine running at less than 1000rpm, link the F and D terminals of the dynamo together, and connect a voltmeter between that link and a good earth on the engine. Assuming you get a voltage reading, the polarity of that will tell you which way the dynamo is polarised, i.e. if you see the F and D are negative with respect to earth, then it hasn't been converted. But if the voltage is positive with respect to the earth, then it has been converted. Remember that the battery polarity will be opposite to this, i.e. if you see a negative voltage on the F and D terminals the battery needs to be connected for positive earth, and vice-versa. However with a car new to you and a non-runner there is nothing to say that the previous owner fitted a dynamo of the opposite polarity in an effort to correct a charging problem, and when it didn't gave up and sold the car. You can connect the battery according to the dynamo polarity, but that still might be wrong for the tach electronics.

    If you do see a voltage, and slowly raising the revs towards 1000rpm increases the voltage towards 20v (do not exceed 20v), then you know the dynamo at least is working. However if you get no voltage, you are no further forwards without diagnosing what is wrong with the dynamo.

      Which Terminal is Which? July 2009:

    Modern 12v batteries usually have the polarity symbols + and - moulded into the battery top by the respective posts, as well as being supplied with colour-coded caps (red for +ve and blue or black for -ve) over the post (discarded on fitting), and possibly coloured rings around the base of the posts (permanent). But some 6v batteries don't seem to have markings, even current supply. These seem to be the ones with the individual screw caps for the cells of which there are least two designs - the original tar-tops with black caps as well as a more modern smooth-topped battery with coloured caps. My present 6v batteries have a single rectangular cover (red) over all three cells and do have + and - markings. There is a possibility that some makes may have a distinct vertical groove in the negative post (no + or - markings), but this remains to be confirmed. Easy to use a meter to determine polarity - as long as you are sighted and the battery has some charge in it! Other than that all the batteries and cars in my experience have had the posts and connectors of different sizes - positive larger than negative. It's not much by sight or touch, only about 1/20" in diameter, but it makes a big difference if you try to put the negative connector on the positive post (it won't fit) or the positive connector on the negative post (it drops on and is loose). If you do need to test-fit the connectors, make sure you only do one at a time, and only one battery at a time, to avoid reverse connection and the risk of shorts from the loose end of the link cable. When changing polarity always change the connectors as well, junking the cup-shaped type (if you still have them) for bolt-up type, as whilst the bolt-up type can be made to fit the wrong posts it would be rather short-sighted. I've seen a couple of comments from people who have flattened the battery, then charged it up in reverse, which seems a really iffy process to me, if not downright dangerous if someone else should go by any + and - markings for reconnection, boosting or even charging. Also some sources stating that +ve and -ve plates are made of slightly different materials which aid battery performance, which would work against you if the polarity is reversed.

    Polarity Conversion 

    As far as the actual conversion goes I've not had to do this myself so what follows is what I've gleaned from elsewhere. The usual reason for converting is that the owner also wants to replace the dynamo with an alternator for its higher output, or fit modern electronic devices. It's possible to connect a positive earth radio in a negative earth car of course but the case has to be insulated from the car body, and if any exposed part of the radio is at (radio) earth potential there is always the risk that this will be bridged to some other part of the car that is at car earth, which will result in a short-circuit and a blown fuse at best. You can also get inverters which convert polarity, but will need a pretty big output for anything but a basic radio. Of course, if you already have a positive earth radio, you will not be able to use it after the conversion.

    The first consideration is the batteries. Before doing anything else make sure the battery earth connection is the first thing you remove, and the last thing to reconnect at the end. All the batteries I have seen have different-sized posts for +ve and -ve so in theory you cannot connect them the wrong way round, therefore the connectors will have to be swapped over or replaced. The original 'helmet' type that completely cover the post and are secured with a small screw that goes into the post expand and get loose with age and repeated removal and replacement, giving poor connections, and some resort to using silver paper to get a tight fit. Seeing as you are changing the polarity originality is not an issue, so if you haven't already replace these with the bolt-up type which give a much better connection. The other thing with the helmet type is that they are usually moulded on, these have to be cut off and replaced with the clamp on type, which usually have two large screws to secure the cable. This results in shortening each cable by about an inch but that shouldn't be a problem. If it is, then you will have to replace the cable(s). If you already have clamp-up type connectors remove these from the hot and earth connections and swap them over. Unless you have already replaced the twin-6v with a single-12v you will also have to deal with the interconnecting cable in the same way, and unless it can be physically removed from the car and reversed you will have to cut off and replace moulded-on helmet-type connectors, or remove and swap over the clamp-up type.

      If you are retaining the dynamo this has to be repolarised so that it generates the correct polarity voltage. Disconnect the wires from the F and D terminals of the dynamo and with the batteries connected take a jumper lead and connect it briefly between the brown at the fusebox and the F terminal of the dynamo so as you see a small spark. Just one flash is enough, then reconnect the dynamo.

      Cars after 64 had the electronic tach and this has to be converted too. You have to get into the case, find the supply and earth wires from the case to the circuit board, and reverse the connections. But note that some cars (e.g. a 67 B belonging to John Schroeder) have the circuit board screwed to the case and pick up the earth connection this way. In this case you have to isolate the circuit board from the case, move the original 12v supply wire from the terminal on the case to the body of the case, and provide a new wire from the earth connection on the circuit board to the 12v supply terminal on the case. John intends to publish notes and pictures of this on the Chicagoland MG Club website. In all cases you have to reverse the direction of the current pulse through the pickup and this also varies. Originally positive-earth cars had a tach with an external pickup and a continuous white wire comes out of the harness, through the pickup twice (i.e. one turn) then back into the harness. With these carefully note the route the wire takes now, remove it, and reverse the direction of the wire through the pickup, but keeping everything else the same e.g. the position of the loop. However there seems to be another variant with a short flying lead through the external pickup, terminated with two male bullets. In this case the harness should have two female bullet connectors, making it very easy to do this part of the switch. Tachs for negative-earth cars up to 1972 all have the pickup inside the case, with male and female bullets on the back of the case, and female (from the ignition switch) and male (to the coil) bullets on the ends of the harness wires.

    Added December 2009: It's frequently stated that when changing the car's polarity you should also reverse the coil connections to keep the polarity of that and the HT spark the same. I usually mention it when the subject comes up, but you do end up with slightly less HT voltage than before either way, replacing the coil with one intended for negative earth cars would be preferable, see Ignition Coil polarity.

    If you have the heater fan motor with black and green/brown wires these may have to be reversed at the connectors by the motor. If in doubt try them both ways (you can't do any harm) and if one way blows more air than the other that is how to connect it. More detail here.

    Fuel pumps: Original pumps used capacitor quenching to reduce points burning and these pumps work on either polarity. Towards the end of production diode quenching was used which gives improved quenching, and these pumps are polarity sensitive. They will work on the 'other' polarity, but quenching will be reduced and hence points burning will increase. These can be converted quite easily. More recently the quenching component used is bi-directional, and these pumps will work correctly on either polarity. 'Pointless' electronic pumps may not work at all on the 'other' polarity, or may be destroyed. More detail here.

    Finally, whereas the original instrument voltage regulators works on either polarity many replacements contain electronics, and most of these will only work on the correct polarity. They may be destroyed, or not work, on the 'other' polarity. More detail here.

    That's it, unless you have any other electronic devices, which will be aftermarket and so up to you. The only possible other thing might be that the wipers now park in a slightly different place. If it bugs you then move the arms on the spindles. Start the car, check the tach is working, and measure the voltage on the brown at 3000rpm with minimal load. With a dynamo you should see in the order of 14.3v to 15.5v depending on ambient temperature (lower volts at higher temps), with an alternator you should see 14.3v to 14.7v.

    Radio August 2009

    Aerial in front wing

    This is not intended to be a dissertation on all the different types of radio or 'in car entertainment' and how to install them, but touches on one aspect of improving security that might not be immediately obvious.


    As the V8 was my daily driver I installed an 'el-cheapo' radio-cassette from Halfords that had a removable face-plate, and was always diligent about removing this from the car when parked up. At that time the car was parked under a car port in front of my house, and despite there being a security light under the porch and a street lamp right outside I came down one morning to find the screen rubber partially cut away and the glass cracked from top to bottom in two places where 'they' had tried to lever it out. Obviously an attempt to break in, and thinking it was an attempt at theft I bought a wheel clamp. A couple of weeks later I came down to find the 1/4-light levered open, window wound down, glovebox and arm-rest cubby open, and the radio missing. So that was what they were after! The trouble is that so many people are lazy that although they remove the face-plate from the radio they leave it somewhere in the car, so it worth these peoples time to break in as more often than not they will find it (but not mine which was in the house), totally destroying the objective of a removable face-plate! I was very lucky, after the first attack the screen was replaced without loss of NCD, and the second time the only damage was a small tear in the shoulder rail under the 1/4-light where they had levered it open, and a broken 1/4-light hinge. They hadn't even scratched the paint levering the glovebox open. MGBs being what they are I was able to purchase just the broken half of the hinge and replaced that, and glued the tear down. I didn't bother claiming for the radio as it would have affected the NCD.

    I still wanted a radio-cassette, so got another el-cheapo from Halfords, but this time a fully removable one where only the chassis is left in the car. This leaves a gaping hole in the console, and so might still attract attention from people expecting it to be left in the car somewhere, but I had another idea up my sleeve! I still had the blanking plate from before I fitted the original radio, which fixes in the console with two flattish clips attached to the back of the blanking plate, that can swivel round to lock behind the back of the console. I bent these into a sort of U-shape so instead of locating behind the console they now fit into the chassis, gripping it top and bottom to hold the blanking plate in place. Even though it is only a friction fit it has never come loose. So now, if anyone does peek in to check out the radio, to all intents there isn't one installed (despite the aerial) so it isn't worth breaking in to look for it. You may well be able to fit one over the top of a radio where only the face-plate is removed, but I'll leave that up to you. I also had an all-singing, all-dancing alarm installed with the usual ultrasonic and perimetric (door, bonnet and boot to you and me) sensing plus a dual-zone microwave unit which will set off the main alarm if anyone gets in the car, and also sounds a warning beeper if anyone gets too close to the outside. But that is another story.

    Quite apart from the security issue technology moves on, and although the quality of tapes was perfectly adequate for the noisy driving environment of the MGB it was a fiddle copying CDs to tapes so I bought a portable CD player with cassette attachment slot that allowed me to play direct from CD via the radio. fast-forward another few years, and it's all about MP3 now, and the ability to get hundreds of tracks onto a single device and so not even have to change CDs. I was given a hard-disk MP3 player that is usually used as a personal player i.e. with headphones, but I found the cassette adapter from the CD player fitted the MP3 player as well so that could be played through the radio. That left the original problem with the cassette attachment that although the transfer of the signal is from an electro-magnetic device sitting in front of the playback head rather than tape, there was still an endless loop of tape driven by the capstan wheel to keep the spool wheels turning. This is nothing to do with playback per se, but some cassette players will stop or go into reverse if one or other of the spool wheels stops during playback. No problem with that, but it was very noisy. I tried opening it up and lubricating the moving parts with powdered graphite but it made little difference. Not knowing whether mine was one of these auto-reverse or stop players I decided to remove the tape altogether, and bingo, it just plays as it should with no added noise.

    Relays Expanded March 2009

    Plug-in Relays

    Relays were used at various times in various places on the MGB:

    • The first usage was as part of the D-type overdrive circuit, until 67 and the MkII and 4-synch gearbox.
    • From 1970 until the end of production a starter relay was used between the ignition switch and the starter solenoid on all models.
    • On all V8s (73 to 76) a relay was used in the cooling fan circuit.
    • On rubber bumper GTs up to 76 a relay was used in the heated rear window circuit, then deleted again when the ignition relay was provided in 1977, which effectively did the same job.
    • From 77 (but see below) to the end of production an ignition relay was provided. Originally this powered all the ignition circuits on UK cars, and everything bar the fuel pump, overdrive and ignition warning light on North American spec cars. In 1978 a number of circuits on RHD cars such as the ignition and heated rear window were moved back to the ignition switch, possibly after problems with the relays sticking closed and draining the battery. Although why this included the heater fan and indicators when it should have been obvious if they were still running after the ignition had been turned off, while leaving the cooling fan (which may only come on a short time after parking the car) and the fuel pump on the relay, is a bit of a mystery. Click the link for ignition schematics .
    • One as-yet unresolved oddity concerns MGBs for North America. The Parts Catalogue and other sources show a 'battery cut-off' relay for the 1976 year on, Part No. 13H9475 and also an 'ignition switch' relay Part No. AAU 3334 for the 1977 year on (when all models got one). However no schematics I have seen show both these relays, and none are shown for the 76 model year in North America as they no longer had the GT so no HRW relay. For 1977 and later the catalogue lists no less than four relays, including an HRW relay and an ignition relay apparently for all versions but when the ignition relay was provided the HRW was deleted. This catalogue again shows the 13H9747 'battery cut-off relay' for North America, which suppliers show as a cooling fan relay, but 4-cylinder cars never had a relay controlling the fans.

    Originally of the Lucas 6RA rectangular metal can type, but you need to be careful with these if replacing them as there are many different types, and in some cases you need to make sure you get the correct replacement. Basically the starter relay is designed for intermittent usage with a low contact resistance to supply the high current required by the pre-engaged starter solenoid, and has a winding resistance of about 40 ohms. The others are designed for continuous operation with a winding of 75 ohms resistance. If you use an intermittent-type relay in a continuous application it will overheat. Using a continuous relay for the starter is less of an issue but may eventually burn its contacts, which will eventually go high-resistance and cause starting problems. Note that when relays get old their contact resistance increases, and on high-current applications like the twin V8 cooling fans this will also cause the relay to get hot. An important thing to note is that if you replace your inertia starter with a pre-engaged you should also consider installing a relay at the same time to protect the ignition switch against the higher solenoid current. One way of doing this is to leave the original solenoid in place and use that as the relay, as per the relevant schematic here.

    As I say there are very many Lucas 6RA relays - 6v, 12v and 24v as well as many different 12v types in addition to the ones mentioned above, you need to compare reference numbers when replacing, don't just go by the '6RA' and the terminals. Having said that many types are suitable for a number of applications, but you need to check the terminal labelling carefully and change wires over by terminal designation and not physical position. These are the MGB variants:

    Part No.
    Lucas Nos.
    56341733243JSRB1134 terminal/spade40 ohm20 ampsintermittentStarter relay
    BMK68533302BSRB1114 terminal, 5 spade76 ohm20 ampscontinuousD-type Overdrive, HRW
    UKC514633188HSRB1023 terminal, 4 spade??continuousV8 cooling fan

    At the time of writing (September 2021) suppliers are showing starter relay 142169A and some images show this as having a double-spade on C1 i.e. for the brown wire. This makes it an SRB111 for continuous operation rather than SRB113 for intermittent operation. The difference is that SRB111 has a higher resistance winding so won't close the contacts as quickly and as hard as the SRB113, which with the high current of the starter solenoid (an initial 30 amps) may cause some contact burning over time.

    4 terminal 5 spade types have a double spade on C1 which is useful for daisy-chaining a circuit to another component without cutting into the wiring.

    The V8 cooling fan relay is an oddity with only three terminals, one being common to both the winding and the contacts, with the missing W2 terminal being connected internally to C2. The idea is that the temp sensor is used to send an earth to W1, with 12v on C2, and the output to the fan motors on C1. Browsing it seems this relay was commonly used as a horn relay on motorbikes, but also on classic Ferrari, Daimler/Jaguar and Rover. There are a few NOS versions around (£130 from a Ferrari supplier, anyone?) indicating it was designated SRB102, but it doesn't seem to be in current production, all the new relays I have seen advertised with the 33188 number are actually four and five terminal relays. These can be used with the existing three-wire harness connections by jumpering W2 to C2, then connecting the harness wires as before. However that would need a piggy-back connector on C2, so better to get a five-terminal relay with two spades on C1 with one jumpered to W2, and reverse the original C1 and C2 connections i.e. the wire that went to C2 now goes to the second spade on C1, and what was on C1 goes to C2.

    However I suspect the V8 relay was replaced by a more conventional 4-terminal relay during production. The reason being the 12v to C2 came from the green circuit fuse, which meant that circuit was powering all the fused ignition circuits including the HRW and the fan relays. This puts a huge current on that fuse and I suspect it suffered from overheating, so they substituted a 4-terminal type with 12v from the brown at the fusebox connected to C2. The drawback with that is that it makes the fan circuit unfused, so I have added an inline in that brown wire. North American cars didn't have a relay despite having the same twin cooling fans, but in that case the fuse was replaced by a self-resetting thermal cut-out, so I suspect they had the same overheating problems there as well.

    More info on Lucas relays here.

    The starter and OD/HRW types have the same configuration of two winding terminals (W1 and W2) and two contact terminals (C1 and C2). The V8 cooling fan relay is a one-off in that it only has three terminals, W2 being connected internally to the C2 terminal hence no W2 terminal. Unlike the other types, in which the winding wires can be reversed, or the contact wires reversed (but winding wires can't be swapped around with contact wires!) on the V8 cooling fan relay the green wire must be connected to C2 and the black/green wire to C1 or the relay won't operate. See also the schematics in electric cooling fans for how to use a conventional 4-terminal relay in place of the original V8 3-terminal cooling fan relay.

    From January 1976 Part No. CHM68, Lucas 26RA 12v 20A cylindrical relay SRB402 with bracket, was used for the starter relay, and AAU3334 for the ignition relay on UK cars from the start of the 77 model year. These use the modern terminal numbering, see below. There only seem to be four variants of this relay, the others being 12v 20A double-normally open, a 12v 20A changeover, and a 24v 10A changeover. The 77 and later Parts Catalogue shows 'Relay - battery cut-off' 13H9475 for the USA and Canada, how this differed from the ignition relay for other markets I don't know, currently suppliers show it as the Bosch cube-type, i.e. it could be the Lucas SRB520 28RA type.

    Lucas 28RA 12v 30A SRB520 cube-type were also factory fitment on late cars, and this style are what is commonly available from after-market sources for accessory switching. No less than 26 different types, just one applicable to the MGB, suitable for both starter and ignition. However as the starter solenoid initially takes a calculated 30 amps it might be better to go for the 40 amp SRB537 for the starter relay.

    July 2015:

    Note: Be aware that there are two pin layouts for these relays, pins 30 and 86 can swap positions. This is significant as 86 is one side of the operate winding and 30 is usually the 12v source to the load. Reversing these can cause weird results. Initially I only found one reference to this - by Vehicle Wiring Products, although it is only detailed in its printed catalogue. However although their web site allows you to order Type A or Type B only Type B shows the terminal layout. The choice is only available with their basic four-terminal 12v relay, their other types (e.g. fused, dioded) are to the Type B layout which is said to be a more logical arrangement. Maybe only the basic 4-terminal type were available before it had been decided that Type B was preferable, so these later types were never made in Type A and are all Type B. I got caught out by this when buying a replacement relay for a commercial headlamp relay system where one dip didn't work, swapped the relays over (which plugged into wired sockets) and the fault moved with the relay so decided the relay was faulty, but the new relay didn't work either! Testing with first principles with a voltmeter, and connecting the 12v source direct to the output wire all indicated the wiring was correct. In desperation I looked at the relay numbering on the base, and spotted the difference. Mentioned it to a pal who had the Vehicle Wiring Products catalogue, he looked it up and found the reference to the two types. I altered the wiring on the one relay socket, but it offends me as the two sides or beams are now different. Checked some eight relays I have dotted around various places and find I have a mix of types. However none are in sockets, so I've always connected the wiring to them directly i.e. looking at the terminals numbers. It's something you would have to be very careful about when replacing plug-in relays anywhere, on modern cars for example.

      Subsequently I came across this from 12 Volt Planet which covers it along with much other information about these Bosch-type relays, saying that the change was made to put the operate terminals on one pair of opposite sides, and the contact terminals on the other two opposite sides, to make visualisation of the connections easier.

    If you don't want to keep with the 6RA and 26RA types for originality the modern black cube relays will be at least as good if not better, 12v items are rated from 20A to 70A. Cube relays come in a variety of contact configurations as well as the basic single-pole normally-open type which is used in all MGB applications except the V8 cooling fan relay. If using an alternative 6RA or modern relay in place of the V8 cooling fan relay at the very minimum you will need to connect the green wire to one of the winding terminals as well as one of the contact terminals. Some types of these modern relays also have integral fuses, which can be no bad thing for accessories on the lightly-fused MGB. However it is no advantage on the HRW or V8 cooling fan relays as the supply to these is fused already (the green circuit). Another variation includes a diode across the winding (see 50 amp Sealed Automotive Relay With Diode) which will protect the circuit operating it. Present stock brake light switches are said to be so poor that as well as not being man enough to operate the lights they need this diode or they still fail from the back emf generated by the relay. With this type you need to connect the power to the winding the correct way round or it will present a short to the operating circuit, although there is a variant of this with a second diode in series with the winding protecting the parallel diode from reverse connection! Yet another variant has a resistor across the winding, these aren't polarity sensitive but don't give as much quenching of back emf as the diode type. Some have a plastic mounting bracket moulded into the casing, some have a slot for an optional metal mounting bracket, and some have no provision for mounting and these are usually plugged into sockets on modern cars. The mounting bracket bolt can be used to provide an earth for the relay where this is required.

    The contact numbering of modern relays is different from the originals. On the originals W1 and W2 are the Lucas winding connections, C1 and C2 the contact connections, on all bar the V8 cooling fan relay as described above. The equivalents on late MGB cylindrical relays and modern cube relays are 85 and 86 for the winding, and 30 and 87 for the contacts. On the basic single-pole, on-off relays as used on the ignition and starter circuits it doesn't matter which way round the two winding connections go, or which way round the two contact connections go, but you mustn't mix up the winding and contact connections. Having said that the convention is that terminal 30 is where the 12v (brown) supply is usually connected to, and 87 feeds whatever the relay controls. Some cube relays have five terminals, the additional terminal in the centre being a normally closed contact 87a, or an additional normally open contact also 87, in which case it will be important to get the three contact wires on the correct terminals. Les common are relays that have diode protection on the winding, to prevent damaging voltage spikes being reflected back into whatever has operated the relay. With these it is important to get the winding terminals the correct way round as well as the relay is polarity dependant. Failure to do this could well damage the relay, and/or whatever is operating the relay, and/or blow a fuse, or the relay may not operate at all.

    You may well wonder at the weird numbering instead of the more logical W1 and W2 for the winding and C1 and C2 for the contacts, but it is part of international standard DIN72552 for automotive components ('DIN' stands for 'Deutsches Institut für Normungstandard' or German Institute for Standardisation), but only relays are likely to be applicable to MGBs. Even then, you will see the format has been changed for relays, with 87 replacing 30 or 51 as the common contact and 87b replacing 87 as the normally open contact. 87a remains as the normally closed contact, where provided. However all the relays I have bought in recent years still use the 30 and 87 convention for 'common' and 'normally open'.

    References: Comprehensive Lucas switchgear catalogue containing information on switches, relays, flashers, both classic and modern, 136 pages, 7MB. Another Lucas relay and switchgear catalogue but including fuseboxes, some duplication with the above, but only 43 pages, 2.8MB.


    This block diagram originally developed by Graham Moore gives a simple but clear overview of the main parts of the MGB electrical system. However there were some 18 variations over the years, both by era and market, but this represents probably the most common arrangement. For detail of a particular circuit you will have to refer to the sections below.

      Many components share wired earths going back to a common body earthing point as well as many branching points including bullet connections. Earth faults can cause some very strange interactions and knowing which components share earths can help track down the source of a problem. Earth paths are not depicted on the simplified Autowire drawings so I have started extracting them from the Leyland drawings and including them at the end of each page that lists the wire colours and functions for each year.

      See also these redrawn schematics from Dan Masters. Capable of being enlarged by several times, they are also laid out so that generally the circuit elements are physically closer together and not placed more or less where they would be on the car. This results in much less wiring snaking all over the place and so are easier to 'read'. They are based on the Workshop Manual, Bentley and Haynes diagrams and so have the same limitations of particularly the later diagrams in Haynes where several slightly different eras of circuitry diagrams are combined into a single diagram, and some of the minor and late changes seem to have been missed altogether. However because the Workshop Manual and Haynes also act as 'layout' drawings they have all the branching and common connection points which are great help in locating wiring faults, including showing earth connections that come from the physical mounting of a component and wired earths, something the Masters simplifications don't have. OTOH the factory drawings are not without errors such as showing early rubber bumper cars having the front parking lights and the indicators in the same housing whereas by that time the parking lights had moved into the headlights, and even when showing that correctly for 1977 cars it doesn't show that the front indicators had wired earths, which all rubber bumper types did.

    The Masters drawings are also confusing because the first batch are numbered as in the Workshop Manual but don't have the index so it's not obvious which market (North America or UK) each is applicable to, you have to look for subtleties like whether it has a brake balance test and warning circuit or not. It's only towards the end that the title box tells you the market, but there is another batch in the middle that doesn't have either! However every one has a sheet number, so the following table lists all three types of designation and confirms which market it is for. Clicking the link for the model will show the diagram full-screen. You should notice the cursor displays a magnifying glass with a plus symbol - position this over a part of the circuit you want to examine more closely, left-click, and it will zoom in to more than double size for even greater clarity. Use the scroll bars to move around.

    62-64 MGB11AllNot 62/64 as shown
    64-67 MGB22AllNot 64/67 as shown
    67/68 MGB33UKI.e. includes 68 models built in 67, ditto other drawings
    68/69 MGB44UK
    69/70 MGB55UKNot 68/70 as shown
    70/71 MGB66UK
    71/72 MGB1111UK
    72/73 MGB1414UK
    73/74 MGB1616UK
    73/74 UK MARKET MGB29UKElectrically identical to Sheet 16
    74 1/2 - 76 MGB1818UKNot 75/76 as shown
    75/76 UK MARKET MGB31UKFunctionally identical to Sheet 18
    LATE UK MARKET MGB33UKThis is an amalgam of several small differences in 77, 78, 79 and 1980 models from Haynes.
    67/68 MGB77North America
    68/69 MGB88North America
    69/70 MGB99North AmericaNot 69/71 as shown
    71/72 MGB1212North AmericaWithout seat belt warning
    71/72 MGB1313North AmericaWith seat belt warning
    72/73 MGB1515North America
    73/74 MGB1717North America
    73/74 US MARKET MGB30North AmericaFunctionally identical to Sheet 17
    1975 MGB W/PERIOD WARNING19North America
    1976 MGB W/CAT CONV21North America
    1976 MGB W/O CAT CONV22North America
    1977 MGB W/CAT CONV23North AmericaOmits the ignition relay
    1977 MGB W/O CAT CONV24North AmericaOmits the ignition relay
    1978 & LATER MGB25North AmericaShows the coil powered from the fusebox when it should be with the white on the ignition relay
    LATE US MARKET MGB32North AmericaThis is an amalgam of several small differences in 77, 78, 79 and 1980 models from Haynes.
    MGC - US MARKET27North America

    Seat Belt Warning

    A fairly straightforward system was used on North American cars in late 1972 and 73 covering both driver and passenger seat belts. A very much more complicated system was used for just one year in 1974, reverting to a simpler system, covering drivers belt only in 1975 for the remainder of production. UK cars got a slightly simpler version in 1977 for the remainder of production, also covering just the drivers belt. The American system included an audible warning if the keys were left in the ignition with the drivers door open.

    North American 1972-73: If the ignition was on, the car in any gear, and the drivers seat belt was not fastened, there was a continual audible and visual warning. Additionally if the passenger seat was occupied and their seat-belt not fastened the same warnings applied. Independently of this if the drivers door was opened with the keys in the ignition, in any position including completely off, there was the same audible warning but no visual.

    North American 1974: A rather complex interlock system requiring a box of electronics with no less than 12 connections plus 10 other components was installed at the behest of the American authorities. One of these components was a 500mA fuse feeding the electronics. This lasted just one year as reputedly American manufacturers complained that the requirements were too complex to implement! With this system there was a drivers seat switch as well as the passengers. Much as before under the appropriate conditions the audible and visual warnings would sound, but additionally the starter circuit was interrupted to prevent starting of the car. There was the same gearbox switch as before, which probably means you can only start the car in neutral, so preventing it leaping forward if inadvertently left in gear. Additionally one has to sit in the seat, then fasten the appropriate belt, then turn the key to crank before the starter will operate, to prevent people leaving the belt fastened behind the seat. If you stall the engine it can be restarted immediately, unless you have switched the ignition off, in which case you must get out of the car and repeat the sit, buckle, start sequence! However there is also a timing delay function, which apparently allows the starter to be operated under any seat-belt conditions i.e. fastened or unfastened, after the drivers seat has been vacated, for a period of three minutes. Which conflicts a bit with the previous sentence. Also if neither seat is occupied one can start the engine by leaning in and turning the key, which would help with manoeuvring the car in and out of the garage. However in this case it seems that the gearbox switch is ignored as the instructions warn that gearbox must be in neutral and the handbrake applied. More information on this system can be found here. Although it shares the buzzer with the seat-belt system the 'key in, door open' warning operates independently.

    North American February 1975-on: A very much simplified system, even more so than the original 72-73 system as the only sensor was on the drivers seat belt (presumably passengers are now expendable). This also had a box of electronics but the main purpose of this was to give a limited period audible warning. The electronics didn't have their own fuse anymore, but picked up a 12v supply from the purple circuit instead. This time the 'key in, door open' circuit is connected in to the electronics, which contained the buzzer, but whether this circuit operates the buzzer continually as before or again on a timer as with the seat-belt I don't know. There was no starter inhibition, but there was still a connection from the start circuit to the electronics. This is to trigger the warning if the car is started without the drivers belt being fastened, rather than as soon as the ignition was turned on as previously, as there is no direct connection to an ignition circuit. There was no gearbox switch. The same starter connection was used to test the warning light for the EGR valve service indicator, fitted in 1975 only (Canada) and 1975 and 76 (rest of North America) but may not have been fitted to all cars.

    UK 1977-on: Much like the later American system but even simpler - no 'key in, door open' function, just a seat-belt warning.

    Starter May 2006

    Help! My starter is cranking all the time! On 76 and later models this can be caused by the 'brake test' diode having gone short-circuit. On all models it can also be caused by failure of the ignition switch, a sticking starter relay (1970-on), sticking solenoid, or chafed wiring.

    Model Variations
    Fixing bolts
    Earth Straps
    Rubber Bumper 'Coil Boost' System August 2014:
    Mechanical Problems
    Electrical Problems - slow cranking
    "It Won't Start!"
    Modern Starters - 'Geared' vs 'Hi-Torque'
    Changing an inertia starter to a pre-engaged
    Jump Starting
    V8 Starter

      Schematics Note: Automatic cars have the White/Red wired via the combined reverse light switch and automatic transmission safety switch on the gearbox. While the automatic gearbox was an option ALL cars had a bullet connector in the white/red starter solenoid circuit in front of the toe-board and below the heater shelf. The automatic sub-harness connected here for the transmission safety switch.

    Inertia Starter (remote solenoid, to 67)
    Pre-engaged starter (attached solenoid) 12v Coil (chrome bumper 68-74, not V8)
    Pre-engaged starter (attached solenoid) 6v Coil (rubber bumper and all V8s)
    Pre-engaged Starter Replaces Inertia

    Model Variations:

    An M418G inertia starter 13H4561 and a remote solenoid on the inner wing was fitted to MkI cars. MkII and later had a 2M100 pre-engaged starter with attached solenoid 13H6130. Originally the ignition switch operated the solenoid directly on both types, but probably because of the higher current requirement of the pre-engaged starter a starter relay was eventually (1970 models) fitted which has the effect of reducing the load on the switch and its connections. 18V engines had the later 2M100 starter 13H7844. The solenoid on this starter has a 'boost' contact for ballasted ignition systems to aid starting (it connects full battery voltage to the 6v coil) but this wasn't used on 4-cylinder CB cars, only RB. All V8s had the 2M100 starter with the coil boost system - albeit to a different part number BHA5223.

    The 1977 LHD Workshop Manual AKM3524 gives the 'lock torque' current (stalled?) as 463 amps, the current at 1000rpm (cranking?) as 300 amps, and the 'light running' (spinning not cranking?) as 40 amps.

    Clausager and the Parts Catalogue say that a rubber boot BHH790 was fitted over the 4-cylinder (but not V8) starter, solenoid and connections from chassis number 284721-on in May 72. It is no longer shown in the 77 and later catalogue, but some say their 77 and later models have it. It's said to be a right pain to remove and refit, my 73 hasn't had one in my 30-year ownership and hasn't suffered as a result.

    Pre-engaged solenoid: August 2013

    The Workshop Manual covering early models makes no mention of it, but the pre-engaged solenoid has two windings - a pull-in of 0.25 to 0.27 ohms as well as a hold-in of 0.76 to 0.8 ohms. Haynes lists both windings in the sectioned drawing of the pre-engaged M418G starter, but doesn't mention it for the later 2M100 for 18V engines, however it will be the same. This results in an initial current of about 30 amps when power is first applied to the solenoid, dropping to about 10 amps when it has operated. In fact it is closer to 8 amps once the cranking load has been applied to the battery, and its voltage falls to the normal cranking level of about 10v. Brian Shaw reported that the solenoid plunger didn't move when he applied 12v to the larger operate spade and earth to the starter body, even though he could see it was sparking, and he measured 11 amps on it. It was only when he connected 12v to the battery cable stud as well as the operate spade that the solenoid operated (and the motor spun). Bob Davis pointed out these two windings and posted a Bosch circuit diagram of a typical starter and ignition system, click the thumbnail for a simplified diagram of the solenoid and motor and an explanation how the system works. However that doesn't explain Brian Shaw's problem. Regardless of whether 12v is connected to the battery cable stud or not, current will still flow from the solenoid operate spade to the starter body through both hold-in winding and the pull-in winding and the motor - as long as the solenoid is connected to the motor. By not having 12v on the battery cable stud the opposite problem occurs, i.e. the pull-in current isn't reduced to the hold-in value when the solenoid operates, so it could overheat. Brian's problem is more an indication that insufficient current was flowing to pull the solenoid in. The solenoid only operating when 12v was applied to the battery cable stud as well is not logical as until the solenoid operates the battery cable stud isn't connected to anything.

    Fixing bolts: August 2016
    Incidentally the two starter bolts are different on engines attached to 4-synch gearboxes. The upper one goes through the engine back-plate and into the bell-housing, so is longer. The lower goes into the back-plate only so is shorter. If a long bolt is fitted here it can foul the flywheel. However there is confusion over the thread type. The Parts Catalogue indicates they are both UNC thread; Brown & Gammons indicates they are both UNF; Moss Europe indicates the longer upper is UNC and the shorter lower is UNF. Moss makes the most sense - bolts that go into alloy castings are usually UNC, and those that go into steel are UNF.

    Earth Straps: January 2020 Earth straps should be braided to cope with engine/gearbox movement, stranded cable (as used at the battery) will eventually fracture if used at the engine or gearbox.

    Chrome bumper cars have the earth strap round the right-hand (as you look into the engine compartment from the front) engine mount with one end under an engine front-plate nut (one of two) and the other under a chassis bracket nut.

    Rubber bumper cars have it at the gearbox end as the engine mounting arrangement is completely different. One end under a bolt through the rubber mount plate into the gearbox casting, and the other end under the nut that secures the mount stud to the crossmember, and as such much less accessible.

    See below for how to check the condition of battery and earth connections. A bad engine/gearbox strap can result in smoking/damaged accelerator, heater and choke cables as well as slow cranking and difficult starting, and I have heard of one case where a braided clutch hose (why?) burst.


    Mechanical Problems: Inertia starters rely on the pinion being 'thrown' into engagement with the flywheel as the motor starts to spin, and it can stick and fail to engage, also only just engage where it can 'jump out' again just as it starts to take the load of the engine, resulting in a whining motor and no cranking. The books say the spiral gear and fine spring should be scrupulously clean and not oiled, but in my experience this causes them to stick as much as over-oiling. Just a drop of light oil on the spiral gear, distributed by working the gear, and any excess wiped off, seems best. The pinion can also jam in mesh with the flywheel after a failed start, and this can prevent any further cranking. This can usually be cleared by putting the car into 4th gear (not 1st!) and rocking it back and fore until it 'clonks' out of engagement. Sometimes the motor has a square shaft sticking out of the back-plate and this can be turned with a spanner to 'wind it out of engagement' and clear the jam. By contrast the pre-engaged starter uses the solenoid to move the pinion into engagement with the flywheel immediately before power is applied to the motor, and the likelihood of jamming with this type is greatly reduced. The pre-engaged does have its own failure mode however, and this is on disengagement after starting. Whereas with the inertia type as soon as the engine starts to spin faster than the motor the pinion is thrown out of engagement with the flywheel, with the pre-engaged the disengagement only occurs when the ignition switch returns from the 'crank' position to the 'run'. There have been cases on modern cars where the ignition switch has failed to return when released by the driver the starter remains energised and engaged with the flywheel, and eventually overheats, catches fire, and had burnt out the car! I've not heard of this on an MGB, though.

    Electrical Problems - slow cranking: As well as a weak battery this can be caused by bad connections in the cranking circuit. The Lucas Fault Diagnosis Service Manual states:

    "The acceptable volt-drop figure for most circuits is 10% of system voltage (1-2v on a 12v system) but there are exceptions to this rule as in the case of the starter circuit where the maximum voltage drop is 0.5v." The first thing to do is measure the voltage on the battery posts (not the clamps or connectors) while cranking - each battery in turn and adding them together for twin 6v batteries. If you see much below 10v then the batteries are weak, otherwise check for bad connections as follows (assumes negative earth, for positive earth cars change each reference of positive to negative and vice-versa). What you are going to do here is measure how much voltage is being 'lost' at bad connections in a circuit, which reduces cranking speed but more importantly reduces voltage to the ignition system, rather than measure the absolute voltage between a terminal and earth.

    Ideally we want to test the 12v circuit between the battery post and the and the solenoid stud - meter positive on the 12v post and negative on the solenoid stud for negative earth cars, reverse for positive earth cars. Again these voltage measurements are taken while cranking, but instead of a meter with manual range selection being set to its 12v scale, it should be switched to a low voltage scale.

    However the solenoid stud is not easy to get to, particularly on the V8 where it is covered with a heat-shield. But by unplugging the alternator plug and using the brown wire in that, you are effectively measuring the voltage at the solenoid stud. Except on the V8 - where the browns go to a battery cable stud under the toe-board, and a short length of battery cable goes from there to the starter. This will give the true voltage at the toe-board stud, which still leaves the potential (ho ho) for losses between there and the solenoid stud.

    But! There is another dodge, and that is that when V8 and rubber-bumper 4-cylinder solenoids are operated and powering the starter, they are also connecting solenoid stud voltage to the ignition ballast bypass wire that goes up to the coil +ve. So removing this from the coil and connecting your meter to that tests the voltage inside the solenoid, and includes any voltage being lost in the battery stud half of the solenoid contact. There could be more voltage lost in the starter half of the solenoid contact, but unless you can get at the link that goes between the solenoid and the starter motor itself you won't be able to test that.

    For twin 6v batteries also measure between the two link cable posts and add that to the losses measured in the 12v and earth circuits to get the total losses. Note that the meter polarity shown is correct for the negative earth system depicted.

    The earth circuit is tested with the positive probe on the starter body and the negative on the battery earth post (for negative earth cars, reverse for positive earth), and checks the engine/gearbox strap as well as the battery earth strap. You will obviously need a long wire for one of these connections on an MGB.

    The individual readings will tell you which of the two (or three) parts of the circuit are giving you the greatest losses. An analogue voltmeter is preferable for these tests as a digital meter may give wildly fluctuating readings while cranking. Disconnect the coil to prevent the engine from starting.

    In a perfect world you would see 0v while cranking on both tests. But even with cables and straps of this size and good connections there will be some resistance, and hence some volt drop, but ideally it should not exceed 0.5v in either path. With freshly cleaned connections you should be able to get it down to a couple of tenths of a volt in each direction. If you get significantly more than 0.5v you have one or more bad connections, and by using the same technique of looking for lost voltage at various connections in a circuit you will be able to determine those that are causing the biggest volt-drops. These can typically be the battery post connectors, with the older cup-style battery connectors in particular, the earth strap where it bolts to the battery box, and either end of the engine/gearbox earthing strap. In any of them you could also get bad connections where the cables and straps attach to their connectors. Incidentally make sure you do have an earthing strap either around the left-hand front engine mount (CB cars) or round the gearbox mounts (RB cars) or your starter current will be returning to earth via the heater and accelerator cables, heating them up and possibly damaging them in the process.

    Also test the link cable between twin-6v batteries in the same way, i.e. between the two posts, and the cable from the remote solenoid on the inner wing and the starter motor for the earlier inertia starters. You can also test the remote solenoid by putting the meter between the two studs. However this will show 12v immediately, dropping to the 'lost' voltage in the contacts when you turn the key to crank. If your pre-engaged starter with the attached solenoid has an exposed link between the solenoid and the motor as some do, you can check that solenoid as well.

    Rubber Bumper 'Coil Boost' System: August 2014
    Rubber bumper cars and all V8s have a 6v ignition system for running, but the coil voltage is boosted to full battery voltage during starting. This makes starting easier and can make the difference between starting and not starting under certain conditions.

    The system works in normal running by feeding ignition voltage to the coil through a ballast resistance concealed in the wiring harness, such that half the voltage is dropped across the ballast resistance and half across the coil. The coils on this system have half the primary resistance of 12v ignition systems - about 1.5 ohms as opposed to about 3 ohms, and are known as 6v coils.

    For starting there is an additional contact on the starter solenoid which is connected direct to the coil +ve. When the solenoid operates as well as powering the starter, it also feeds battery voltage out on this additional contact. With a decent battery you should get 10v while cranking, which boost the coil voltage from the normal 6v running level to 10v during cranking, which gives a much fatter spark. This boost voltage is disconnected as soon as you release the key and stop cranking, if you ran with this voltage on a 6v coil you would overheat it and rapidly burn out the points.


    It seems many geared and 'hi-torque' starters supplied for the MGB still don't have the extra contact on the solenoid which boosts coil voltage during cranking, meaning you either have to dispense with the coil boost feature or replicate it with an alternative or additional relay, or possible a diode if you know what you are doing! Click the thumbnail for three options.

    A couple of people have asked why the bypass circuit doesn't come from the existing contact on the starter relay and the answer is that Messers Ohm, Volt and Amp won't allow it! With the coil +ve wired to the solenoid contact on the relay you create a network of resistances instead of two simple series circuits and they interact with each other to affect the voltage that is available to the coil, reducing it from 6v to about 1.5v which isn't enough for ignition. A secondary effect is that the current through the ballast resistance would increase from about 4 amps to 7 amps almost doubling the heat that it would have to dissipate, and a tertiary effect is that the solenoid would have some current passing through it all the time.

    I recently started getting hot-starting problems on the V8, first wondering if it was a batch of dodgy fuel, but when it happened again two or three tankfuls later I wondered whether the coil boost circuit was operating. I connected an earth to the coil -ve effectively shorting out the points, and connected a volt-meter between the coil +ve and earth. When turning on the ignition I saw 6v which was what I expected. However when turning the key to crank, instead of seeing about 10v, the voltage dropped to 5v i.e. half the cranking voltage, so the coil boost circuit wasn't working.

    I got under the car and found the coil boost wire was broken between where it came out of the harness and where it went to the spade on the solenoid. This wiring was damaged when I got the car, there is supposed to be a short sub-harness on the starter and a 2-way connector joining it to the main harness, but this was missing and a dodgy join made instead. I'm not sure why it needs this as both solenoid spades are accessible even with the heat-shield in place. When I replaced the starter in 1999 I repaired it as best I could - I had to change the spade as originally it was a small spade to distinguish it from the standardised solenoid operate spade, but it seems that rebuilt starters have two standard spades. However since then the insulation had hardened and cracked in a couple of places and allowed engine movement to flex the conductors which fractured them.

    I made a better repair, removing the heat-shield and convoluted sheathing that covered the battery cable plus the two wires. I sleeved all the wire that came out of the harness with two layers of heat-shrink for strength, and soldering the end of that to the tail from the starter, putting two layers of heat-shrink over the join as well. Tested before refitting the convoluted sheathing ... and still no boost! This time I put the meter right on the solenoid spade with the wiring removed, and still no boost, so there is a problem with the solenoid. The question then was, whether to remove the starter and investigate it, or use one of my alternatives until the engine comes out for a replacement clutch or whatever. Having replaced the starter previously I know I could get at everything relatively easily, so opted to take the starter out, which only took a few minutes.


    The V8 has a curious arrangement of a stud under the toe-board with the battery cable attached on the top, then a few inches of battery cable from the bottom of the stud to the starter. This together with the sub-harness containing the solenoid operate and boost wires means the starter can be removed and refitted with these three still attached to it - why, I don't know. Maybe it is so you can fit the heat-shield before the starter, which is a bit of a fiddle, although I have been able to remove and replace it with the starter in-situ.

    With the starter on the bench a couple of Allen screws removed and a nut terminating the starter feed to the second stud slackened the solenoid comes away. There are two Phillips screws holding the 'plastic' end-cap that carries the two studs and the two spades to the end of the solenoid, but there are wires from the solenoid that come through the cap and have to be unsoldered from the operate terminal and the starter stud, and fortunately my iron is up to the job. Flicking molten solder off, then levering up the ends of the wires, allows the end-cap to be removed.

    I can immediately see what the problem is! There is a large copper bar that bridges the two studs when the solenoid operates, and the boost terminal has a small copper contact that sits between the two studs and should be contacted by the copper bar at the same time. However, the contact is bent back, so the copper bar will never touch it. This lies under the copper bar, so it is impossible that my dismantling has damaged it in any way, it must have been like that from the beginning. It obviously was never tested, and although I tested the starter before fitting I only checked that the pinion moved forward and spun. I didn't check the boost contact - "Of course that will work ..." yeah right.

    So I straightened the boost contact, and adjusted it such that the copper bar touched that before it reached the two studs. Refitted the end-cap but didn't solder the wires yet, and with a continuity meter checked that when the copper bar was moved manually by pushing a bar down the middle of the solenoid the boost contact and the two studs were all connected together. Re-soldered the wires, and fitted the solenoid to the motor. Another test this time with 12v between the battery cable stud and the solenoid body, then bridge the battery cable stud to the operate spade, first to check the pinion comes forward and spins, and secondly to check that voltage appears at the boost contact - all good.

    Refit the starter to the engine, attach the battery cable and the two wires but leave the sheathing and the heat-shield for the time being, and redo the original test i.e. monitoring the coil voltage before and during cranking - success! Refit the sheathing and the heat-shield, test again - still good.

    So the question is, will this overcome the hot-starting problem, which in any case is still down to unknown causes, as there obviously has been no coil boost function for 14 years. But the hot starting has only been an issue for two or three months, and seems to be associated with hot weather.

    October 2018: It seems to have gone as suddenly as it came, nothing since the summer of 2014, including in the very hot weather we have experienced this year. There have been several complaints of 'vaporisation' or 'vapour lock' in various fora and Enjoying MG, with those reporting it claiming it is common. Not only has it not happened to me, but on various runs in hot weather this year I've not come across any stranded MGBs - including organised runs with dozens of MGBs and Midgets taking part! If you get the problem, then there is a fault on your car that can be fixed without resorting to modifications. The one possibility I will acknowledge is that excessive fuel height in float chambers can expand when turning off a hot engine, and rise enough to run out of the jet into the inlet manifold, resulting in a rich mixture which DOES affect hot starts. That can be caused by incorrect float height, and for those that experience it during a long idle it may even be the float valves are not fully closing off when they should, and letting in more fuel that is being used at idle (see this test). That will gradually raise the fuel level in the jet, with liquid fuel eventually running in to the inlet.

    'Hi-Torque' Starters: Be careful with these! I've seen some and they sit between the original and the geared starters. They have a different internal construction that gives more torque in a smaller and lighter unit than the original starters, but they are not as efficient as the geared starters. However these days geared starters are also described as 'high torque', so you need to be careful what you are buying. In general non-geared starters seem to have the motor in line with the pinion, and the solenoid attached to the side. Most geared starters have the solenoid in line with the pinion and the motor to one side, and the solenoid is about the same size as the motor. Price should be the most obvious difference.


    Modern Geared Starters:
    Coil-boost considerations on rubber bumper cars

    Within the last few years 'geared' starters have become available for the MGB as an aftermarket item. These simultaneously reduce the current drain on the engine and spin the engine faster - I've seen claims of double the cranking torque for nearly half the current drain - which both aid starting and increase battery life, they are also smaller, lighter and quieter! In fact the solenoids on these are usually larger than the actual motor, and it is the solenoid that is inline with the pinion and not the motor. There are a number of basic types of starter from different manufacturers, with a variety of different adapter plates to mate them to the MGB bell-housing. Some come with a captive bolt ready to go into the bell-housing as one of them is shrouded by the motor. Others are assembled differently and both bolt holes are accessible. Some have a slotted top hole which makes it easier fit the motor - you start the bolt first hook the motor onto it, then while that takes the weight of the motor you can start the second bolt. Others require you to support the weight of the motor whilst trying to get one of the bolts started. They are available to replace both inertia and pre-engaged starters, because although the inertia starter pulls the pinion into engagement with the back of the flywheel and the pre-engaged (including these geared starters) push it into engagement from the front, the earlier flywheel has the teeth cut properly on both faces of the flywheel so will accept either type.

    September 2021: A New Kid in Town (to me) is the Powerlite Micro-Starter, described as 'epicyclical' but it looks lie a conventional starter in that the motor is in line with the pinion and the solenoid is on the side, whereas previous geared starters are the other way round. But that is because an epicylic gearbox has the input and output in line, like the overdrive, whereas the other geared starters only have a single idler gear between the two shafts so they are offset. Very light at 5.2lb, but also very expensive at more than 50% dearer than other geared types, which themselves are typically three times dearer than a 'lightweight' modern conventional starter. 'Lightweight' is by comparison to the original MGB starter, they are available but at twice the price of the modern they can only be of interest to 'purists'. Very confusing information in the MGOC ad for the Powerlite starter as well as on the Powerlite site itself:

    • MGOC states 'dual polarity' but for the MGA, MGB and other MGs of that era they have always been dual polarity.
    • MGOC states they are for 1968 and later but Powerlite themselves sell them for all MGBs, but there are different versions for Mk1 with inertia starters and Mk2-on with pre-engaged.
    • The difference between inertia and pre-engaged starters for the 4-cylinder MGB is that the former have 9 teeth on the pinion and the latter 10 teeth (V8 have 10 teeth).
    • At the same time as the starter changed from inertia to pre-engaged the electrics changed from positive earth to negative earth.
    • Powerlite for the inertia version say 'negative earth' but MGB with inertia starters were positive earth originally, so does that mean the inertia version can only be used on converted cars?
    You must get the correct type of geared starter though, as the pinions have different numbers of teeth:
  • Inertia starters (MGB to 67 and all MGC) have 9 teeth - note that the geared starter replacement for this is a pre-engaged starter, not an inertia starter.
  • Pre-engaged starters on the MGB have 10 teeth.
  • The factory V8, even though it is a pre-engaged starter, also has 9 teeth.
  • An early example I tried on the V8 was very poorly manufactured in that the adapter plate was only held to the motor by three self-tapping screws and some super-glue! Needless to say it broke free within a few days, so look for some substantial bolts connecting the plate to the motor. While it was on though it was remarkably quiet, so much so that the first time I turned the starter I though the motor was just spinning without being engaged with the flywheel.

    Price: Geared starters are the most efficient but whether it is worth paying the very large premium on them is debateable. At the time of updating (September 2021):

    So it pays to shop around. Brown and Gammons and Leacy seem to depict the same light-weight unit as Moss, so hopefully have the coil boost contact for rubber bumper cars as well. This isn't always the case, geared types don't seem to have it, but Moss US seems to include a sub-harness with the solenoid operate wire plus a second dioded wire going to the same solenoid terminal to provide the coil ballast bypass function when starting. A diode is one of three ways of providing the coil boost function if your new starter doesn't have it, as described here

    September 2021:
    Mark Robinson shopped around for a geared starter in America and got one for the same price in dollars as we would pay in pounds, so a bargain. However when mounted using the slotted hole at the bottom which aids fitting, that puts the motor below the solenoid and its connections for the battery cable and operate wire are above the motor and can only be accessed from above. Moss Europe shows the slotted hole on the other side of the solenoid to the motor, which puts the motor above the solenoid, and makes the connections more accessible from below. Another issue is that the battery cable connector is bent at a right-angle originally, but will have to be straightened to fit this starter. So with that and the positioning Mark has made up a short stub between the car's battery cable and brown wires, and the solenoid stud.

    February 2017: I've just had occasion to replace the starter motor on my ZS 180. It's immediately apparent that the new one is much quieter and cranks noticeably faster than the old one. When I first had the car I felt that cranking it sounded much like my MGBs, i.e. significantly noisier than other 'modern' cars heard round and about. It's almost as quiet as a geared starter, but not quite. The motor is externally identical to the modern light-weight versions from the likes of Moss etc., so I'd have no problems about using this type on my MGBs in place of an OE.

     Changing an inertia starter to a pre-engaged: Updated April 2012
    Positive-earth, Mk1 cars used an inertia starter with a remote solenoid operated direct from the ignition switch. For one year negative earth/ground cars used a pre-engaged starter (with the solenoid mounted on the starter) again operated directly from the ignition switch. After that MGBs got a starter relay operated from the ignition switch, which operated the solenoid, which operated the motor. This was done to reduce the load on the ignition switch as the current drawn by the later, attached, starter solenoids is significantly more than the remote type, as it has to push the pinion into mesh with the flywheel as well as close an electrical contact.

    When fitting a later engine to a Mk1 car, or fitting a pre-engaged (any type) starter to a Mk1 engine, there are several possible ways of integrating the new pre-engaged starter with the original wiring:

  • Remove the original solenoid, reroute the original battery cable to the battery cable stud on the new starter, and extend the brown wires down to the new starter. This will work, but requires joints in the wires which is not a good thing, and the original ignition switch will be carrying the current of the new solenoid, which is quite a bit higher than the original, and may burn out the ignition switch.
  • Leave the original solenoid in place, move the starter motor cable onto the battery cable stud of the original solenoid, connect the other end of that onto the battery cable stud of the new starter, and remove the white/red wire from the original solenoid and extend it down to the operate spade of the new solenoid. Leaves the original solenoid but it isn't doing anything other than acting as a connector block, and you still have the problem of joints in the white/red and the full current of the new solenoid going through the original ignition switch.
  • You can add a starter relay to either of the above, which solves the problem of excessive current through the original ignition switch, but you have to find somewhere to mount the new relay and provide three new wires to battery, earth and the new solenoid. The original white/red transfers from the original solenoid to the appropriate terminal on the new relay.
  • In response to someone having starter problems (first continual cranking then no ignition) after fitting a hi-torque starter, Matt Dabney suggested using the existing solenoid as the starter relay, which only involves moving the original motor cable from it's stud on the original solenoid to the same stud as the battery cable (the other end of which goes to what would normally be the battery cable stud on the new starter), then running a new wire down from the now empty motor stud on the original solenoid to the operate spade on the new starter.
  • However the simplest method is to use the original solenoid as a starter relay as above, but leave all the wiring on the original solenoid as it is. The original motor cable goes to what would normally be the battery cable stud on the new starter, and the only other change is to simply connect a wire from that stud to the operate spade of the new solenoid - a distance of about an inch or so. Now the ignition switch operates the original solenoid, that extends 12v down to the new solenoid, which operates and extends the 12v on to the new motor. The only difference to how the factory wired the pre-engaged starter on the later engines is that you won't have 12v on what would normally be the battery cable stud on the new solenoid, but then you don't need there to be as the brown wires are still with the battery cable on the new solenoid.
  • Jump-Starting: Updated December 2011

    Jump Leads
    Starter Pack
    Battery Cable Post in the Engine Compartment

     Never, ever, follow the advice given by a certain contributor to the MGOC magazine and 'clip the ends of the leads together'. It's true there was a drawing showing one lead clipped to the insulation of the other, but the following month it was obvious someone had taken the advice literally and connected the two clips together, destroying a battery. The person involved was very lucky the battery didn't blow up in her face. The contributor than had the unbelievable arrogance to imply that at least she will have learned a lesson!

    Quite apart from the extreme hazard if the advice is misunderstood as in this case, even clipping one end to the insulation of the other is bad advice. The clips have teeth which will bite into the insulation and quite possibly damage it, and why have to cope with two leads at a time instead of just one? You only have two hands, but three ends. So if you clip the two free ends onto one battery or the other, the clipped-together ends will be dangling somewhere, and one of them at least will be live at some point. Far safer to separate the leads if possible and deal with one at a time as below. All the leads I have looked at appear to have two separate cables. If yours have the two cables tied together in someway, such that you can't completely separate the cables, then you should still deal with one polarity of cable at a time, then deal with the other. You will have to watch where the two free ends are dangling, as well as what you are doing with the ends you are dealing with, but at least the dangling bits should be short and they won't be live at any time.

    Jump-starting, or 'boosting' is the act of using another battery - a donor - temporarily hooked up to a car - the recipient - to start it typically when its own battery is flat, the donor battery often being in another vehicle. Great care must be taken when connecting the donor battery, if it is connected incorrectly explosions can occur at worst or electronic components like the alternator destroyed. That said there are a number of myths and legends surrounding jump-starting to be ignored. One is that the arc generated when connecting jump-leads will destroy the diodes in the alternator of the recipient. It won't as long as you connect the two the right way round! The second is that having the donor engine running while cranking the recipient will burn-out the donor alternator. It shouldn't, all alternators have over-current protection built in.

    You can get expensive heavy copper professional leads and cheaper aluminium home-use leads. The former are much more robust, can carry much higher currents and have safety-insulated clips, but the results of connecting them the wrong way round will be much more spectacular! The hobbyists leads have a certain amount of 'fail-safe' in that they cannot carry such high currents so are less likely to result in battery damage if connected incorrectly, but the connections between cables and croc-clips are a bit iffy (they will get quite warm in use) and the clips are usually uninsulated. You will not get as much cranking voltage with the hobbyists leads as with the professional but in my experience it should be more than enough to get the recipient started (6-cylinder BMWs excepted ...).

    Either vehicle can be of either polarity (i.e. either positive or negative earth), but no matter what the polarity of either vehicle the connections are always positive to positive and negative to negative. You must confirm the polarity of both cars before you start. Never assume that colour-coded cables or plastic covers on the battery terminals are a reliable indication of polarity, look for '+' and '-' symbols on the battery case, or coloured rings round the posts. If you cannot see them check with a voltmeter. A voltmeter can also confirm which is the live terminal and which is the earth/body terminal, and even a newly flat battery should have enough voltage in it to indicate polarity. The MGB changed from positive earth to negative earth in 1967, other classic cars may be different, probably all modern cars are negative earth. If the recipient has not run for a long time and the battery has been out of the car in the mean time make sure the battery has been reconnected correctly. The positive and negative battery posts and clamps are of different sizes, but it is possible to force bolt-up clamps (not the 'helmet' variety) onto the wrong terminals given enough brute force and ignorance.

    When connecting different polarity cars together never let metal parts of the cars come into contact with each other or this will short out one of the batteries and cause a very high current to flow, but then we wouldn't let out cars come into contact with anything else anyway, would we? And even on same-polarity cars the potential difference between them can be enough to cause damage to the surfaces in contact. Because MGB starter motor and battery cable are pretty well hidden the usual way of jumping to or from is direct to the batteries even though they are also relatively inaccessible. Note that on a V8 you might be able to use the toe-board stud but I have never done this, and with uninsulated clips the risk of the clip coming into contact with the chassis rail is quite high. If either car has twin 6v batteries you must take careful note of which are the +ve and -ve terminals of the two batteries taken as a single unit and not connect anything to the interconnecting cable that goes between the two.

    Connect both ends of one cable first, then connect the second cable. If you connect both cables to one battery first you might inadvertently bring the free ends of the jump-leads together which will generate a big spark off a fully charged battery.

    You can connect the two batteries together using the jump-leads direct on all four battery terminals, but the risk with this is that if you have got the connections the wrong way round one of the batteries may explode as you are leaning over it. For that reason it may be better to make the last connection to some sturdy chunk of earthed metal like the block. Easy enough on most cars other than an MGB as the battery is usually in the engine compartment, but a bit more difficult when two MGBs are involved. Personally I always tap the last croc-clip on very briefly first to see how much of a spark I get. Connecting a fully charged battery to a flat one will always generate a small spark but the spark from having the batteries the wrong way round is much bigger!

    I've just come across these Kangaroo Safety Jump Leads from Airflow which should help guard against sparks and incorrect connection. They are in two halves, with an interconnecting plug. To use them you part the plug, put the two clips of one half on one battery, then the two clips of the other half on the other battery. Then you look at the LEDs in each half of the interconnecting plug which will indicate whether you have the clips on correctly. If you do, push the two halves of the interconnecting plug together. Could be useful on MGs with two black leads at the battery/ies and no polarity marking symbols or colours.

    I always leave the engine of the donor vehicle running while cranking the other car. This ensures the donor battery is at its maximum voltage beforehand, recharges it during the brief pauses in cranking the recipient, and if one persists in cranking a car that just won't start it avoids flattening the donor battery as well.

    Rather than cranking the recipient you can leave the jump-leads connected for some minutes allowing the alternator of the donor to charge the recipients battery, disconnect the jump-leads then try starting as normal.

    Equal care needs to be taken when disconnecting leads, that they don't hit earthed or painted parts, or short together. Some advice says if a modern car is involved at one end or the other when the jumped engine is running the headlights, heated rear window and heater fan should be turned on full to minimise any voltage surges that might damage electronic units. Additionally some suppliers of electronic ignition systems for classic cars say they should not be jump-started at all or it may damage the module.

    Starter Packs Added February 2014
    There are various types of these containing a full-size battery, with mains-powered charger, and often a compressor, from £50 upwards. However these are pretty bulky and one wouldn't normally carry them round.

    July 2019: I've had my jump leads for probably getting-on for 50 years and having been bought in my impecunious youth they were cheap ones with aluminium conductors and the clamps crimped on. Never terribly effective, and the last time I used them five years ago I had to wiggle the conductors in the clamps to get them to work. Now one of Bee's batteries suddenly failed and all the wiggling and additional crimping couldn't get enough power out of another battery, so Something Has To Be Done. In any event jump leads need a donor car next door, but we do a lot of touring on our own in some pretty remote locations. Capacitor packs need a donor close enough by to charge it up, which leaves lithium jump packs as the only way to be truly self-sufficient. True they have to be topped up every year or so, but that's not difficult. Looking around there are several different capacities but with three cars I need one capable of powering the biggest - Vee, so 3.5 litres minimum, and if you have a diesel in your fleet that reduces the maximum engine size a given pack will power. Halfords do a Noco GB20 for 4 litres (which is the minimum size from that manufacturer although the instructions say not suitable for diesel) at £79 click and collect. I could get it for a bit less mail-order, or alternative products cheaper still, but as it is an unknown quantity to me I want to be able to get a refund with no hassle. It comes half-powered, and took about four hours with a USB connector plugged into my desktop computer front panel to get fully charged. USB sources less than 2.1A will limit the current and so extend the charging time. No direct mains connection but USB mains plugs are available for a few pounds, as are car accessory socket adapters, although note that something described as '5W' is only a 1A source. I then note that the information says 'only suitable for single batteries', but two 6v batteries in series are exactly the same as a single 12v - as long as you connect the jump pack correctly, but that applies to any boost starting and charging method.

    Although by now the replacement batteries had arrived I left the old ones in Bee so I could test the jump pack. Followed the instructions and all seemed when I connected it and switched it on, so went for a start. It cranked well enough and started OK but I must say I was expecting faster cranking with 400Amps, as it was it was slower than the batteries used to be before they croaked. As this was 1800cc I wondered what it would be like on the 2.5 V6, and the 3.5 V8. So I took the earth cables off Vee's battery, and put both of my old jump leads in series between the earth cable and the earth post to simulate a flat battery. Tried to start (without the jump pack!) and barely a groan from the starter. Connected the jump pack (to the CABLES, not the battery!), switched on, and cranked again (cold engine parked overnight) and it spun the engine like billy-oh - noticeable faster than Bee. So that's OK. Did the same with the ZS with the same result, so for some reason it finds Bee harder to turn than the other two. Vee is low compression compared to Bee, but the ZS is higher at 10.25:1 Could be the starter circuit of course - poor connections, but with the new batteries in they whizzed the engine round - also cold and no choke. It's high summer of course so thinner oil even when 'cold', may be slower in the deep mid-winter, and I have to remember to take it with me whichever car we are using. Subsequently towards the end of the summer when the ZS battery had gone down through lack of use it only took moments to get it going. Needless to say I carry it in whichever car I'm in at the time!

    March 2019: When I first wrote this section I had just been made aware of this 'Startmonkey 400' from British Motor Heritage. Claiming to start any car or van and delivering up to 400 amps, with enough capacity for 15 to 20 starts of 6 to 8 seconds each. Small enough to keep in the car, and rechargeable from either the cars electrics or mains. Expensive at £200 though. Now there are many different brands all significantly cheaper, some of them at a quarter of the price at around £50. You do need to charge them periodically to make sure they are ready for use - not much point in spending that much, and carrying it around, only to discover it hadn't got enough oomph when you needed it away from a mains socket. Several of them are capable of being charged from the car's accessories socket as well as the mains, so I don't see why you couldn't keep it connected all the time in the car i.e. fully charged at all times. However if your accessories socket is 'live' all the time as on MGBs from 1972 and some earlier you would need to be sure that the jump pack wouldn't discharge back into the cars electrics and flatten itself. If it is only live when the ignition switch is in the accessories or run position as it seems modern cars generally are you should be fine. Personally I shall stick with my jump leads (replaced with a jump-pack) and mobile phone. Some of the jump packs include a phone recharger, but the first thing I get on the rare occasions I change my phone is a charger that plugs into the lighter socket, and these are usually just a few pounds. Your battery would have to be completely dead, and your phone battery flat, to strand you then.

    There are also loads of capacitor-based jump packs around, see this Google search. These are not intended to hold a charge long-term and be ready for use immediately, but if you have a 'donor' car nearby they charge in a minute or so then can be transferred to the car with the flat battery. A sort-of half-way house between a battery pack and jump leads - doesn't need regular charging like a battery pack, but doesn't need to be right next to a donor car like jump leads and doesn't have the hazards of incorrect connection either. But it does need a donor to be nearby and accessible, so even by that the self-contained battery type are better, and some of them are cheaper too.

    There are gizmos around that plug into both cars cigar lighters and transfer a charge between them without using jump-leads at all, a LED indicating when the recipient has enough charge to try starting it. I don't know whether these can cope with either polarity or can only be used when both cars are negative earth. I also don't know how long they would take to put sufficient charge back into the recipient to allow it to start. When collecting my son's BMW with a near completely flat battery I couldn't even get that to start with jump leads and a donor vehicle, even with the donor engine running, and having left it charging like that for half an hour. In the end I had to call out the AA for their starter pack.

    Finally, if a normally easy starter suddenly refuses to start one day there is little point in cranking it until you flatten the battery. If it doesn't start given double the normal cranking time then you should be checking the ignition and fuel supply. If it is a hard starter anyway, well, if it is an MGB there is something wrong that you should have seen to a long time ago, you are knackering your batteries out of laziness.


    Typical conventional jump-leads
    Lighter-socket jump-leads
    AA recommendations.
    Halfords recommendations.
    UK Health and Safety Executive recommendations (pages 5 and 6, begins at para 24).

    Battery Cable Post in the Engine Compartment June 2020: Given the faff of getting to the batteries in an MGB I've long pondered having a battery cable post in the engine compartment, for connecting a jump pack should it be required. I know some marques have this as standard, and it's 'just' a matter of getting a suitable post somewhere in the engine compartment and a cable down to the starter (or the connection point under the floor on the V8). After coming to the end of working for a month or so painting at a pal's place and the prospect of not having enough to do in the Covid lockdown, I started looking seriously.

    First question is where to mount the post - not much point in buying the makings until that is decided, not least without knowing how much cable will be needed. I don't like drilling holes in bodywork, but on Bee there is a convenient space just aft of the coil, and the clamp bolt can be used to mount a bracket for the post.

    Next what post to use. I Googled various terms looking for one with a cap that would insulate the terminal when not in use, then flip back to connect the jump pack, but the only ones I could find were through-panel and hugely expensive. Eventually I settled for a surface-mount 8mm post with small base as taking up the least space but big enough for starting current - 8mm is close to the battery cable post on the starter. I need something to insulate the post when not being used, and they have various 'boots' that slide onto the cable and fit over the termination. An enquiry comes back with red push-on cover 35mm cable size max, so order both at the very reasonable price of £5 plus £4 P&P, and they arrive in a few days.

    Next a bracket - I used a bit of 5mm aluminium off-cut and made a stepped T-shaped bracket to fit the base of the post, and go under the coil clamp bolt. The step holds the nuts that attach the post to the bracket away from the wing. Measuring from there down to the starter with enough slack to make a couple of right-angle bends comes to about 450mm.

    Unfortunately 12v Planet only have battery cable by the metre i.e. unterminated, so more searching comes up with SplitCharge who have no less than 19 combinations of colour, current capacity, terminal sizes and lengths. 110 amp should be fine for such a short distance, 8mm terminals each end, at £4.41 including P&P, which also arrives in a few days.

    My initial thought was to route the cable down with the others against the firewall then go forwards to the starter along with the brown wires. But that brought it very close to sundry pipes and the clutch slave, unless it had been quite a bit longer. At the starter end it was better if the cable went straight down to the terminal, and I could have got away with a shorter cable. So I end up with six of one and half a dozen of the other where the cable goes back towards the firewall, then angles forwards and down to the solenoid terminal. Engine rocking has to be considered and proximity to the chassis rail and solenoid, but I have some split corrugated sheathing which slides over the cable to protect it at that end.

    Subsequently I fit one to Vee as well, piggy-backing the post bracket on the alarm siren bracket.

    V8 Starter
    Heat Shield

    I have had two separate bouts of solenoid chattering on the V8 a couple of years apart. Both initially were only when the engine was hot, although eventually it was doing it on cold starts as well. In both cases improving bad connections in the brown - starter relay - solenoid circuit cured the problems (for two years in the first case) but eventually I did have to go for starter replacement. I suspect the starter was on the way out all along, the bad connections were just making it worse.

    To my surprise I was able to replace the starter without removing either the tubular manifold or down pipe on the right-hand side, but I did have to remove the rack in order to get sufficient movement with a spanner on the top nut. Subsequently (I tried an alternative starter for a while but went back to the OE item) I used a pair of 3/8" extensions and a universal joint to get to the top bolt between two of the pipes on the manifold, meaning I didn't even have to remove the rack. The situation with the original cast-iron manifolds may be different.

    Replacements: The alternative I mention was one of the 'gear reduction' starters beginning to crop up all over the place. They are much smaller and lighter, in fact the solenoid is bigger than the motor, and bigger than the on the original starter so should be more robust, it being the solenoid that usually fails on V8 starters. The first time I tried it I thought it was just spinning and not turning the engine over as there was no rocking of the engine and no grinding, just a steady hum, but then it fired up. Because of the gear reduction the motor has a lot more torque, hence the smaller size, and spins faster and so take a lot less current which should take a lot less out of the battery at each start. However the connections were in a different place meaning I had to connect the cables before I could fit it which meant lying on my back under the car holding the motor up in the air with one hand, while I attached the cables with the other. There is also no boost contact for the coil on rubber bumper cars and all V8s on the ones I have seen. This last could be simulated with a relay, but with the lower drain on the battery it may not need it. They are about 50% dearer in price though. The problem with mine was that the motor assembly was attached to the adapted plate with just a couple of self-tappers, and needless to say these came loose after just a few days. On another occasion, and with beefier mountings, I could well be tempted to fit one. Be aware that there are after-market starters available described as 'hi-torque' - not all of these are geared, Caveat Emptor. May 2019: It seems only two types of replacement are available for the factory V8 - the original style and geared. Prices are very variable, Clive Wheatley has the original 3M100 type at £120 exchange and the geared type at £252. SC Parts has the original at £230 plus a £264 core charge until you return the original, and the geared at £264.

    Conversions: I've seen a couple of comments now about the starter motor fouling things when a Rover V8 from another application is used for a conversion. On at least one of these the solenoid is on the side of the motor when installed which will definitely foul the chassis rail. It needs to be below as per the original, but to get an original you are faced with finding one from somewhere, maybe to use as an exchange, or fork out nearly £500 as above. In which case it would be preferable for several reasons to get a geared for half that. These geared starters are basically a standard motor on an adapter plate orientated to suit the application, and SC Parts has just such an adapter plate meaning you have the potential of getting a motor elsewhere and modifying it accordingly.

    Switches in General Added May 2009

    There has been quite a bit of comment on mailing lists and bulletin boards for a few years about the poor quality of replacement switches. Probably one of the earliest related to replacement brake light switches failing very soon after fitting. The only 'cure' for this seems to be to install a relief relay, but back EMF from that still causes the problem so protection has to be added in the form of diode or capacitor quenching (see Brake Lights). Adding relays (and fuses) to the headlight circuit is a must when uprating the headlights (see Uprated Headlights), and these will take the load off both the main lighting switch and the dip-switch and their associated connections. They may even be necessary with standard lighting system if you have to replace the switch, I have just found my main lighting switch intermittently failing to power the headlights. This is a 'new' switch from when I restored Bee, and although that was 20 years ago use of lighting has been minimal since.

    Another common problem is with the hazard switch. Not so much with replacement quality this time, as hardening of the internal lubricating grease after many years and little use so that it tends to insulate the contacts. Sometimes flipping the switch back and fore will sort it out, but sometimes only temporarily. I had to dismantle Vee's (in a poly bag to catch all the bits), dig out the old grease and put in some fresh some years ago and it has worked fine ever since. That is with the original style of rocker switch, a friends 78 with the later smaller switches had intermittent heater and hazard switches. I tried dismantling these and cleaning them but the bits inside are so small, fiddly and delicate it wasn't successful and we had to resort to buying new.

    Another quite common problem concerns the overdrive lockout switch on the gearbox. In this case it isn't the contacts that go faulty but mechanical wear in the linkages between gear-lever and the button on the switch causing the switch to be pushed not quite far enough to close and engage OD. With this often by pulling the gear lever around in 4th gear you can make OD engage and disengage at will. This can usually be corrected by an 'adjustment' at the switch. The switch was originally fitted with two fibre spacer washers, and removing one of these usually cures the problem. Unfortunately the switch is awkward to reach, particularly on 4-synch cars which only have a small removable panel on top of the transmission tunnel. Remove the centre arm-rest, remove the screws from the centre console, pull back the tunnel carpet, and remove the small access panel. But even then it isn't easy to get at the switch. You can get a bit more space by undoing the rear crossmember bolts and allowing the tail of the OD to rest on the fixed crossmember, being careful not to damage the speedo cable.

    One thing to be aware of is that testing switches with an ohmmeter is not good enough. Ohmmeters only pass a minute current through a circuit - especially digital meters, MGB switches don't have gold contact surfaces, and so they will oxidise especially if not used for a while, which presents a resistance to an ohmmeter. However when carrying their normal current this will burn through any slight surface film, and the circuit will usually work as they should. Because of this the only valid test for detecting bad connections is looking for volt-drops where there shouldn't be any when the circuit is carrying it's design current. April 2017: Even overnight can be enough for the switch resistance to start getting erratic. When Bee's OD started dropping out after a few miles the first thing I did when back home was to check the current by inserting an ammeter at the manual switch, which was correct at about 800mA, and double-checked by measuring the solenoid resistance at about 15 ohms which is also correct. After leaving it overnight I went straight for the resistance check and was surprised to see it varying all over the place as I moved the gear lever round, anywhere between 15 ohms and over 200 ohms. But powering the solenoid with an ammeter in series I got the correct 800mA, and when testing the resistance again I got a consistent 15 ohms. Passing normal current through the switch had 'cleaned' its contacts.

    Screen Washers

    Washers schematic
    Nozzles and valves
    Convert manual to electric
    Washer bottle decals

    Originally a manually operated pump, utilising a rubber 'bulb' in an alloy housing which was compressed by a plunger. The back of the rubber bulb has a plastic end-cap with two ports for the tubing. No valves here, it relies on the valve(s) in the bottle and tubing to push fluid to the screen when the plunger is operated and pull it from the bottle when released to recharge the bulb.

    Electric washers were provided on North American models from the 1968 model year and UK models from 1974 1/2 i.e. the start of rubber bumper production. The exception is the V8 which had electric from inception in 1972. The controlling switch is on a column stalk with the wipers being a push-button on the end, the motor is mounted by the water bottle. The motor is polarity sensitive so needs to be connected the right way round to pump. For some reason the factory decided to connect this 'the other way round' i.e. instead of the switch controlling the 12v supply to the component which is permanently connected to earth, the switch controls the earth and the motor is permanently connected to the green (fused ignition) supply. Thinking about it this probably avoids having two wires going up inside the stalk. A earth can be picked up from the body of the stalk if it is metal, so only one wire is needed. Funnily enough they went the other way with the horns in 1977 - they had always been backed by 12v and a switched earth sounded them until then, after that the horn button put out 12v and the horns were backed by a earth from their physical mounting. So that needs two wires up the stalk but saves a long-ish run of (purple) wire from the fusebox to the horns.

    Note that from 1971 for the remainder of chrome bumper production and all V8s the electric washers (and wipers and heater fan) were powered from the accessories position of the ignition switch via a white/green to an in-line fuse under the fusebox, and then via a green/pink.

    Update January 2010: Karl from Ohio reports that he found the black earth wire with a stripped end hanging loose at the base of the stalk, and eventually that the stalk itself (which is a tube with the green/black running up inside) can be pulled out of the main body of the switch, has a groove in the splined end of the stalk tube which the earth wire conductors can be laid in, then stalk with earth wire pushed back into the body of the switch.

      The nozzles were different between roadster and GT until 1978 - separate single nozzles for right and left on roadsters, a single item with two nozzles on GTs, then two plastic nozzles on all cars form 1978. The Parts Catalogue shows 'filter' 13H 7846 for all cars, which one supplier converts to GWW601, which several suppliers show as a 'foot, filter and valve' which goes in the washer bottle. However the catalogue also shows 'valve-line' 13H 6501 which is an in-line valve i.e. a second valve, which some have found behind the dash right up by the nozzles, possibly only GTs with the dual nozzle item.

    August 2021: Prepping Bee for the MOT I found the (manual) screen washer didn't work - some gurgling but no spray. This is something that gets used as regular as clockwork - once a year for the MOT! Wondered if the bottle had developed a leak but no, still some fluid in there and no gunge. Had another more vigorous go and no better, but this time when I stopped I noticed water in the pipe going back towards the bottle. What about the one-way valve(s)? There is a component on the end of the pipe in the bottle that looks like a valve, and looking at the business end the bit that contained the two flaps was at an angle in the housing. Pressed that back into place ... and Bingo! I replaced the bottle over 30 years ago and replaced the plain water with screenwash fluid probably in 1995, but other than that it's not been touched and always worked - weird!

    Convert manual to electric
    The details of the washer bottle end will depend on what pump or pump kit you get, and on the face of it the switch can be positioned anywhere including in place of the manual pump. But David Birkby wanted to keep the appearance of the dash the same so modified the manual pump to accept a simple 'push for on, release for off' switch. Since then I have done the same for Bee following a problem with the 'foot valve' in the bottle even though that was easily resolved.


    One speed or two?
    Parking Systems
    Motors, gears, arms and blades
    Intermittent Enhancement
    Lucas Wiper Catalogue


    MkI Roadster Single-speed
    MkI GT Single-speed
    MkII and later two-speed

    Note 1: From 1971 for the remainder of chrome bumper production and all V8s the wipers (and heater fan and electric washers where fitted) were powered from the accessories position of the ignition switch via a white/green to an in-line fuse under the fusebox, and then via a green/pink.

    Note 2: In 1970 (North America), 1974 (V8), and from the start of rubber-bumper production for remaining cars the wiper switch moved from the dash-board to a column stalk. Some time later possibly for the 1977 model year on the wiper stalk incorporated a flick-wipe feature. The wire colours remained the same through all these changes, Note 1 excepted.

    The 1977 LHD Workshop Manual AKM3524 gives the 'normal' speed current as 1.5 amps, the high speed current as 2 amps, the normal speed wiping as '4.6 to 52 rev/min' (presumably 46 to 52 sweeps per minute), and the high speed as 60 to 70 rev/min, both after 60 seconds, and presumably a wet screen.

    One speed or two?  Rewritten February 2012

    There were three different wiper systems - MkI roadsters, MkI GTs, and MkII-on.

    The MkI roadster used a square, single-speed motor 17H2013/57H5599/GEU714 with a basic internal parking circuit, three wires, and a simple on/off switch with just two wires.

    The MkI GT had a round single-speed motor 27H6409 with a more complex parking circuit that involved the manual switch, with four wires at the motor and three at the switch. There was an adapter harness that allowed its different motor to use the roadster harness for three of the wires, the fourth wire running direct from the motor to a different manual switch (13H 1909) with an extra terminal. The Leyland Parts Catalogue for the Mk1 GT says to use GEU708 as an alternative to 27H6409 - GEU708 is the Mk2 two-speed motor but it is 'plug compatible' with the Mk1 GT albeit only giving the 'standard' speed unless a wiring and switch modification is made.

    In May 67 the MkI GT switch was also fitted to the MkI roadster for standardisation, with the extra 'park' terminal left unused.

    In Nov 67 all MkII cars got a new round two-speed motor 37H2732/GEU708 with a similar parking system to the MkI GT, with five wires at the motor. The switch was changed again to give two 'on' positions and a park contact, making four wires at the switch.

    Upgrading Mk1 roadster to two-speed
    Two aspects - motor mounting and electrical. As the 2-speed 14W motor and its mounting arrangements differ to those of the original have a look at this document from Colyn Firth regarding this job on his MGA. For the electrical side Colyn chose to provide relays so he could continue to use an original MGA pull-switch (albeit the three-position lighting switch) instead of mounting an MGB toggle switch elsewhere. For the MGB you will need the Mk2 toggle wiper switch (BHA4786, Lucas 35927 57SA) with six spades giving two 'on' positions as well as the 'park' function. Ideally you would have the wiring connector to fit the connector block on the motor, but could get away with insulated spade connectors on each wire. You need to add two more wires from the motor to the switch - for the second speed and the park function. Strictly speaking you should correct the polarity by providing a 12v supply to the switch in place of the earth, and use the motor connections to 12v and earth as for the later cars. It will work without but in that case you must reverse the 12v and earth connections at the motor from those shown in the schematics for MkII cars or it will blow the fuse. Also with an earth from the switch and 12v at the motor the two-speed motor will run backwards, being permanent magnet stator rather than wound. But that will happen on the many MkI cars that have had their battery polarity reversed, and I've never heard of any problems with the wipers subsequently.

    Upgrading Mk1 GT to two-speed
    Much easier as the motor mounting is the same and the motor is 'plug compatible' with the existing wiring, you only need to provide one additional wire for the second speed, plus the switch as above. But Keith Evans contacted me with the following:

    "I have just replaced the wiper motor on my early GT fitted with a single speed round motor type 12W, now sadly NLA. My local stockists told me the later 2 speed round type 14W was interchangeable. It is except for one problem, you need to also change the Gear Wheel, as the later housing is smaller, and will not allow the original to fit. I replaced with the later type of Gear Wheel and now all is well. This has a dimple on the Gear Wheel for parking, which moves a plunger type switch to park, as opposed to the original interrupted 3 contacts type. The power plug is the same, however the high speed contact and the additional wire for the fast speed is not there, so the wipers only run at standard speed, as the original wiper motor did. My next job is to fit a 2 speed switch, and another spade into the Wiper motor plug. although then not original, I think in modern conditions, Safety will be improved. The circuitry corresponds to the 1967 GT schematic, and the later 2 speed schematic. And the difference is the latter has the Blue and Green wire from Pin 8 of the switch to the missing spade in the plug." The appropriate gear wheel needs to be obtained as well because they differ between roadster and GT as well as with other marques and models, and motors are usually supplied without.


    Mk1 roadster systems had a basic normally-open 'on-off' toggle switch to connect an earth to the motor to cause it to run, and a simple parking system that when switched off allows a park wiper contact and arc on the motor to keep an earth connected to the motor until it reaches the park position.

    Mk1 GTs had a later system with a more consistent parking method that used a more complex switch and an extra wire - the 'park' wire. It's possible this was found necessary on the GT with its longer wiper blades and arms as at speed they could interfere with the driver's view.

    Two-speed systems use a similar parking system to the GT but with a three-position manual switch with a power wire, 'standard' and 'fast' wires, and a 'park' wire. that connects 12v to the standard and fast speed windings as required, but when switched off an additional wire on the switch - the park wire - is connected to the standard-speed wire. With the wipers not parked the motor park switch connects 12v to this park wire, which with the manual switch in the 'off' position is connected to the standard speed wire and causes the motor to continue to run. When the wipers reach the park position the motor park switch disconnects 12v from the park wire (and hence from the standard speed winding) and connects an earth to it instead. This parking system ensures that the motor stops dead which stops the blades in a more consistent position, the earlier system was affected by whether the screen was wet or dry. Originally a toggle switch, from 1972 it was a rocker switch, then rubber bumper 4-cylinder cars and all V8s had a column switch.

    1977 and later models use basically the same system but with an additional 'flick-wipe' feature.

    Stalk Switch:
    V8s and rubber bumper had a column stalk switch for the two-speed wipers, overdrive and screen washer of two different types, for 77 and later it incorporated a flick-wipe function.


    1977 and later models came with a flick-wipe feature by moving the stalk down (on RHD cars, LHD used the same switch mechanism but on the other side of the car so flick is up and the continuous speeds down). The manual switch was basically the same but with an additional non-latching contact to connect 12v to the standard-speed winding while the stalk is held down, then parks as normal when released, click the thumbnail for details.

    Be aware that replacement switches from some suppliers have been incorrectly assembled so the flick-wipe function does not work, click the thumbnail for details. Simon Holland received two incorrect switches from one supplier before receiving the correct item from Moss UK. Most of the Google images I have been able to find show the incorrect assembly, Moss, Brown & Gammons and Midland Sports and Classics are correct (at the time of writing, in September 2019 of those three only MSC shows the correct orientation), but it is relatively easy to tell the difference from suppliers photos.

    To add flick-wipe to MkI roadsters you simply need a non-latching normally-open contact (SPST) to connect a momentary earth to the black/green wire for the wipers to complete a single sweep and then park.

    The MkI GT and all MkII two-speed wipers need a more complicated circuit because of the different parking system, suggested wiring is shown here.

    Parking systems

    Which side do you park?

    The square MkI roadster motors have a earth supplied from the manual switch and 12v at the motor. The parking circuit consists of a moving contact on the large gear wheel running on an arc which has a break where the wipers are required to stop. The contact is connected to earth and the arc is connected to the motor, bypassing the manual switch. Thus when the wipers are away from their park position the motor has an alternative earth supply to keep it running until the park position is reached. This parking mechanism is fairly crude in that the inertia of the motor and wipers allows them to 'over-shoot' a little meaning the actual stopping position varies with conditions, i.e. a dry screen will stop them sooner compared to when the screen is fully wet. The wire colours and functions are as follows:
  • Green - 12v supply to motor
  • Black - earth to motor for parking circuit
  • Black/Green - standard speed connection to motor earthed by manual switch

    The round MkI GT motor parking system differs in that it stops in a much more predictable and controlled fashion. The parking circuit consists of a normally-closed contact at the manual switch and a change-over switch at the motor which consists of a segmented disc with three sections that rotates with the large gear wheel, and three fixed brushes that are part of the connector plug. With the manual switch on an earth is connected to the red/light-green 'run' wire that goes to the motor to operate the motor. When the manual switch is turned off the red/light-green is disconnected from earth and connected instead to the black/green 'park' wire that goes to one contact on the parking disc. With the wipers not parked this part of the disc is connected to an earth on another part of the disc to keep the motor running. Just before the park position is reached the earth is disconnected from the segmented disc to remove power from the motor, but inertia allows the motor to continue to turn as it slows down, then shortly afterwards 12v is connected to the third section of the segmented cam, which is picked up by the black/green wire, which goes back to the manual switch (off) then comes back to the motor on the red/light-green wire, which effectively short-circuits the winding. The motor now has 12v both sides which effectively stops it instantly. The theory behind this is that when power is disconnected from a motor it has inertia and continues to spin as it is slowing down and in the case of the wiper motor this means that the blades can stop in different positions according to how wet the screen is and vehicle speed. While it is spinning down it becomes a dynamo generating a voltage at its windings, and by shorting out the winding the dynamo is effectively being asked to supply a very high current which puts a heavy load on it, which is why it stops very quickly, and this gives it a consistent park position. The wire colours and functions from the Workshop Manuals are as follows:
    • Green - 12v supply to motor
    • Black - earth to motor for parking circuit and manual switch for running
    • Red/Light-green - running connection to motor earthed by manual switch in the 'on' position, connected to the park circuit in the 'off' position
    • Black/Green - motor to manual switch for park circuit
    • Note the adapter harness has the first three as short wires between the main harness and the motor, and the last is a long wire from the motor to the manual switch.

    February 2014:

    Click the thumbnail for how to test this motor with the five-pin (but only four wires) connector .

    MkII and later: The round two-speed motor on these cars has a similar park principle to the MkI GT, but now the motor is backed by earth and the manual switch puts out 12v instead of earth to run the motor. The manual switch again has the normally-closed contact which connects the standard-speed wire to the park wire when the manual switch is in the off position. But now there is second changeover switch on the motor, that supplies 12v to run the motor when the manual switch is off and while the wipers are not parked, and an earth in the park position to short-out the motor and stop it rapidly as before. The wire colours and functions are shown here.

    However this motor is not without its own confusions as although there was only one part number for the complete motor assembly there were at least two different types of park switch. The motors could be suffixed A, B etc. up to F or maybe higher. A and B have a screw-on park switch 37H 2734, examples of D and F have the more common clip-on park switch 37H 6784. The brush plates also differ.

    Which side do you dress I mean park?  Added October 2008
    This question seems to crop up from time to time, particularly in North America. Parking in front of the driver seems the most logical, as they will clear the driver's view first which is safer when first turning them on in the event of sudden spray being thrown across the screen. However that needs the arms to be angled such that the blades lie flat across the bottom of the screen, straight arms would be across part of the drivers view, and indeed some photos of early cars do show the blades like this, particularly the 64 car on the front of Clausager which looks like it could have straight arms. FWIW modern cars seem to park on the passenger side, but with their much deeper screens they can have much longer arms and blades which move about 90 degrees i.e. from the horizontal parked position against the bottom edge to the vertical position against the right-hand edge as compared to the 106 degrees of roadsters and 115 degrees of GTs. This gives a far greater proportion of swept area, leaving little more than a small arc at the top corner on the passenger side.

    It seems quite clear that RHD cars always parked in front of the driver i.e. on the right-hand side. Many North Americans say theirs also park on the right, some say they park on the left, and some say that when ordering new arms they get the 'wrong' ones i.e. angled for parking on one side when they need the other. All the photos of LHD cars in Clausager show them parking on the right, but interestingly the Coune Berlinette on page 107 is parked on the left even though it is an RHD! It's not difficult to get them parked on the 'other' side - on the earlier round motors with the park switch on the domed cover over the main gear you can slacken the cover screws and rotate the domed part by 180 degrees.

    On the later round 14W motors with the plastic park switch and connector block combined you can dig the plastic cam out of the back of the main gear and reposition it. The intermediate GT system is significantly different to either the earlier single-speed or the later two-speed. May 2009: Bob Muenchausen has contacted me to say that 20 years ago all he did to change sides was to simply rotate the wheel boxes 180 degrees so that the rack drives them from the top instead of the bottom, and reset the arms - brilliantly simple! You have to remove the rack and tubes from the wheelboxes to do this, so obviously easier with the dashboard out for example during a rebuild as Bob did. It is possible to get motor, tubes and wheelboxes out and back in as an assembly (a pal has done that for other reasons) in order to do that.

    November 2021: A really strange thing happened to the MGC of Geoff Thirlby in that the blades suddenly started parking on the other side! I listed a number of things to check, even though Geoff said there had been no changes made to the car, and I couldn't see how any of them could happen by themselves. Then Geoff removed the large gear from the motor to look at the parking cam.

    His is quite different to the other one I had seen, and with Geoff's I can imagine that if the plastic gear started sliding down the shaft of the cam plate the location pegs could become disengaged, which would stop the blades while the gear carried on turning. Then the pegs could re-engage 180 degrees out and the blades carry on but would park at the other end of the sweep. It seems unlikely, but what else could it have been apart from the garage pixies, as Geoff said? He was able to slide it down and turn it through 180 degrees to correct the problem. On the other type of gear its probably impossible for the cam to move round the gear and re-engage, but depending on how the gear is attached to the cam plate that could still move as Geoff's seems to have done.

    However that's not the whole story, you have to consider any angle in the arms which tilts the blades one way or the other. Whether the blades park in front of the driver or the passenger, you would always want them to sweep right down parallel to the bottom edge of the screen in front of the driver or he will have quite a large unswept arc in front. This means that when they park in front of the passenger, they will be angled up across their view, and partially across the drivers when they look across - see the photos of my V8 and roadster temporarily stopped in this position. Bob tells me that when he changed his parking position he replaced the arms which is fair enough, but he used generic arms which could be angled either way, something I haven't come across before.

    Going back to Clausager's photos, these all appear to be triple wipers, and that raises an interesting point. North America changed to triple wipers in November 68 as the authorities required a greater proportion of the glass to be swept (the relatively short screens necessitating short blades to avoid going off the top of the screen, which left large areas either side and between the swept arcs). As this moved the left-hand arm closer to the left-hand side of the car, more of the glass would have been swept that side, so the blades could park in front of the passenger but still sweep an 'acceptable' area in front of the driver. This changes the unswept area from being an arc at the top corner of the screen to a triangle at the bottom corner. The latter may be smaller, but to me having a clear screen to see people and objects at street level is preferable to being able to see things up in the sky (traffic lights excepted)! Whereas previously - for some of the time at any rate - LHD cars seem to have parked in front of the driver, it looks like cars with triple wipers changed to park on the right-hand side i.e. same as RHD cars. This must have been the case from April 71 as RHD cars got the same arms as LHD cars, and as the arms have a bend at the top to allow the blades to park against the bottom edge of the screen, they must have both parked on the same side, i.e. the right. From the Parts catalogues it would also seem likely that LHD GTs always parked in front of the driver, as the gears and arms were always different between LHD and RHD, LHD were common to all markets, and they never had triple wipers.

    Before triple wipers the situation is less clear. Up to February 63 the complete wiper system was the same for both left and right-hand drive. If the change of parking side on the early motor was very easy i.e. just turning the park switch dome over the main gear through 180 degrees, then possibly the factory made the change themselves. And if the arms were straight it wouldn't have made much difference either way. In February 63 the arms changed to have stronger springs, and also changed to be different between RHD and LHD. In November 67 motors, gears (which now controlled the park position) and arms were all different, and if the parking side wasn't different before it almost certainly was now. That takes us up to November 68 when North American cars triple wipers, and got different arms to other LHD cars. The difference in arms continued up to April 71 when the North American arms were fitted to RHD cars. It wasn't until September 74 when all LHD cars were produced to North American spec that other LHD cars got the North American arms.

    The MG Enthusiasts bulletin board has a pretty comprehensive series of photos of cars from 1962 to 1981 and these roadsters make interesting viewing:

    YearUSAPark sideEuropePark side
    1962not available  DenmarkDriver
    1963Originally Californian,
    exported to Norway
    Passenger GermanyDriver
    1966not available HollandDriver
    1967USADrivernot available 
    1968USADrivernot available 
    1972LHD V8 (Switzerland,
    Holland, Germany)
    This indicates - when examples are available from both locations, that all LHD cars with two wipers i.e. up to and including 1968 parked in front of the driver. Also that for the 1969 year again all LHD cars got triple wipers that parked in front of the passenger.

    The confusing thing is that even when North American cars got triple wipers, and changed over to park on the right when they weren't before, they kept the same motor and gear as before - according to the Parts Catalogue, that is. Other LHD cars had the same motor and gear as North American spec cars. Where the Parts Catalogue gives the North American items a different part number to other LHD items and with a 'Safety' marking this is more likely to indicates a difference in material or construction methods and not function. The other thing to be aware of when comparing part numbers is that roadster wiper motors from November 67 to June 76 had suffix letters A, B and D. The motors were less the gear, the gears did not have suffix letters i.e. were just RHD or LHD, but the park switch (and brushes) had one part number with an A and B suffix and another with the D suffix or no suffix. The Catalogue has a note saying reference must always be made to the suffix letter to ensure the correct part is received, so it is probably the suffix letter that determines which side parking takes place. Unfortunately it doesn't say which suffix letter applies to which situation, i.e. RHD, LHD North America or LHD elsewhere. RHD cars had the same motor as LHD, but their own gear, from November 67 until the end of production. Other part number changes will be due to the change from bright arms and blades to matt-black, and there also seems to have been a change in position of roadster wiper spindles which required a change in arm and/or blade length.

    Looking at GT pictures on the MG Enthusiasts bulletin board only one LHD (undated but between a 75 and a 77, the cars all being in date order) has the wipers on the right i.e. in front of the passenger, at least one LHD from each year having them in front of the driver.

      The full (as near as I can judge) list of part number changes:

    Change-point MotorCommentsGearArmsCommentsBlades
    HN3-101May-62HN3-6916RHD/LHD17H 2013Use GEU 71457H 5589BHA 432110.25" arms, 10" bladesGWB 202
    HN3-6917Feb-63HN3-138400RHD57H 5599Use GEU 71447H 530737H 4952Heavier (13 oz) wiper armsGWB 202
    HN3-6917Feb-63HN3-138400LHD57H 5599Use GEU 71447H 5307BHA 4396Heavier (13 oz) wiper armsGWB 202
    HN4-138401Nov-67HN4-158230LHD NA37H 2732Use GEU 70837H 3046BHA 4816 GWB 202
    HN4-138401Nov-67HN4-167576RHD37H 2732Use GEU 70837H 3045BHA 4814 GWB 202
    HN4-138401Nov-67HN4-167576LHD not NA37H 2732Use GEU 70837H 3046BHA 4816 GWB 202
    HN4-158231Nov-68HN4-164063LHD NA37H 2732Use GEU 70837H 304613H 5460Triple wipersGWB 202
    HN4-164064Dec-68HN5-294250LHD NA37H 2732Use GEU 70837H 3046BHA 4913Magnatex arms instead of LucasGWB 141
    HN4-167577Feb-69HN5-246076RHD37H 2732Use GEU 70837H 3045BHA 4914Magnatex arms instead of LucasGWB 141
    HN4-167577Feb-69HN5-294250LHD not NA37H 2732Use GEU 70837H 3046BHA 4915Magnatex arms instead of LucasGWB 141
    HN5-246077Apr-71HN5-294250RHD37H 2732Use GEU 70837H 3045BHA 4913LHD NA arms fittedGWB 141
    HN5-294251Aug-72HN5-410000RHD37H 2732Use GEU 70837H 3045BHA 5201Matt black arms and bladesGWB 216
    HN5-294251Aug-72HN5-360300LHD not NA37H 2732Use GEU 70837H 3046BHA 5203Matt black arms and bladesGWB 216
    HN5-294251Aug-72HN5-410000LHD NA37H 2732Use GEU 70837H 3046BHA 5201Matt black arms and blades (3)GWB 216
    HN5-360301Sep-74HN5-410000LHD not NA37H 2732Use GEU 70837H 3046BHA 5201NA arms fittedGWB 216
    HN5-410001Jun-76onRHD37H 8221 37H 3045BHA 5201 GWB 184
    HN5-410001Jun-76onLHD37H 8221 37H 3046BHA 5201 GWB 184
    Change-point MotorCommentsGearArmsCommentsBlades
    HD3  RHD27H 6409Use GEU 708
    (see note)
    27H 6420BHA 454612" arms, 11" bladesGWB 142
    HD3  LHD27H 6429 27H 6424BHA 454812" arms, 11" bladesGWB 142
    HD4-138401Nov-67HD4-158230RHD37H 2732Use GEU 70837H 3047BHA 481713" bladesGWB 143
    HD4-138401Nov-67HD4-158230LHD37H 2732Use GEU 70837H 3048BHA 481913" bladesGWB 143
    HD4-158231Nov-68HD5-296000RHD37H 2732Use GEU 70837H 4308BHA 488113" bladesGWB 144
    HD4-158231Nov-68HD5-296000LHD37H 2732Use GEU 70837H 4309BHA 488013" bladesGWB 144
    HD5-296001Aug-72onRHD37H 2732Use GEU 70837H 4308BHA 5205Matt-black 12" arms and 13" bladesGWB 217
    HD5-296001Aug-72onLHD37H 2732Use GEU 70837H 4309BHA 5204Matt-black 12" arms and 13" bladesGWB 217
    All  RHD37H 2732Use GEU 70837H 4308BHA 5205Matt-black 12" arms and 13" bladesGWB 217

    Note: GEU 708 is a two-speed motor but is 'plug compatible' with the Mk1 GT wiring albeit giving only the 'standard' speed without modifying the wiring and switch.

    GT wipers have a wider sweep angle than roadsters and this is set by the position of the crank pin on the main gear - that for the GT will be further out from the spindle than the roadster. Roadsters were 106 degrees, GTs were 115 degrees originally then 125 degrees for 1969 models on according to the Parts Catalogue, but suppliers indicate this change was much earlier. It looks like the main gear is stamped with the applicable sweep angle.

    December 2011:

    That leaves the angle the parked blades make to the screen. Clausager shows a 1964 Tartan Red on page 17 with the right-hand wiper at an angle to the screen, but the inner end on the screen surround so it can't go down any more. However the left-hand wiper is cocked way up, and is clear of the surround, so I'd be looking if that arm could be moved on the spindle by one spline. The 68 MGC on the facing page has them lower, with the right-hand pretty-well flat, and the left-hand angled but much lower. Most other images in the book have them flat to the surround, and both my cars are like that. I'm pretty sure I have never altered the V8, but following a comment on a BBS I do recall increasing the angle at the blade-end of the roadster arms to make the blades lie flat before repainting them. There have also been reference to 10 or 12 degree arms, and 20 degree arms, the difference being the larger angle makes them lie flat where the smaller angle doesn't. GT arms and blades are longer and the spindles are positioned differently to the roadster partly because of the deeper glass, the overall effect being that the arms need less of an angle for the blades to lie flat to the lower edge of the glass. Where they park in front of the driver, parking flat is desirable, and I adjusted my roadster arms as follows: With the edges of the blade-end of the arm clamped lightly between the jaws of a vice, I gripped the flat sides just above the jaws with a pair of large pliers so stop the arm turning over and buckling, then pulled the splined-socket end of the arm towards me. I didn't bother about the angle, just did each until the blade lay flat, only took a couple of goes. This may chip the paint on painted, but that can be touched-up if you aren't repainting them anyway. For bright arms probably best to use plastic vice jaw inserts and similar in the plier jaws, but then again they can be polished.


    Slow or non-running
    Poor clearing
    Flying off
    Parking on the wrong side

    One thing that plagues BMC rack-and-pinion wipers is excessive slop after many years use. I used to think that this was all due to wear in the wheel-boxes and rack, and no doubt some is. If you think about it, the wheel-boxes consist of a gear wheel in which slightly less than half is ever used, and only one side of the rack is ever used. So if you remove the wiper arms, disconnect the rack at the motor and withdraw it until the wiper spindles are free, rotate the wiper spindles through 180 degrees, turn over the rack and put everything back, you should be running on unused portions of the wiper boxes and rack. I tried that on my V8 but if anything it has made things worse - maybe a PO had already done it - so I had a careful look at the rack. It consists of a flexible-ish straight wire with a stiff wire wrapped round it in a spiral to form the 'teeth' of the rack. It looked to me as if the pitch between the turns of the spiral that ran in the wheel-boxes was greater than elsewhere, not due to wear but distortion, and that would account for some slop. My next task is to see if I can get a new rack and try that. In fact shortly after writing this the rack broke anyway! I got a replacement from the MGOC, it had to be cut to the correct length, and it did indeed cure the slop!

    Slow or non-running: Updated September 2008: Another problem is slow running, and that is about the most difficult thing to investigate on the MGB, worse even than slow indicators. This can be caused by dry spindles in the wheel-boxes, some say old stiff grease in the gearbox causes it but I have not experienced this. Worn brushes can also cause it, and also cause intermittent running. A common cause is low voltage at the motor caused by bad connections. As the power has to come from the solenoid on the brown circuit, through the ignition switch (or ignition relay) onto the white or white/brown, through the fuse onto the green (or green/pink) circuit, through the wiper switch to the motor, and from the motor to an earth connection, plus the many spade and bullet connections in that circuit. The problem is that low voltage causes slow running, which causes high current. But mechanical drag also causes slow running, which causes high current, and both cause additional voltage drop. So it is extremely difficult to know whether the cause is electrical or mechanical, especially as the harness plug for the motor is hidden between the motor and the bulkhead and very difficult if not impossible to get meter probes onto. Removing the motor and connecting a good 12v and earth supply to the connector pins will show if the motor itself is the cause, but if not that still leaves mechanical drag from the rack, wiper boxes and blades, or electrical connections and doesn't put you much further forward.

    February 2013: Manek Dubash of Lewes reported on MG Enthusiasts that his wipers weren't working or very slow, the motor got very hot and was blowing fuses. He measured the running current on the bench (i.e. not wiping the screen) at 5.2 to 5.5 amps, whereas the book says it should be 2.7 to 3.4 amps when it is wiping the (wet) screen (on the standard speed if a 2-speed motor). The wheelboxes and rack being attached or not made little difference, neither did resisting movement by hand. He decided to get a new armature as they are only £9.50 compared to £50 for a complete motor (well spotted), and with that fitted on the bench (i.e. no wiper blade load) it was drawing only 1.6 amps on the standard speed and 2.2 on the fast, so the fault was probably a partially burnt-out armature winding. Note that on a stationary motor a typical standard winding measures 1.5 ohms and fast 1 ohm, so it's possible to get a current of up to 14 amps with a stalled motor.

    Failure to park (just stops when the manual switch is turned off) can be caused by a worn park switch in all types of motor as well as disconnected wiring or a faulty manual switch in the case of the later parking system. The park-switch (see left) is in a single unit with the multi-connector plug on the motor and has a nylon peg that pokes through the gearbox casing which is lifted up by a cam on the large gear, the nylon peg can wear down as well as the switch contacts fail. The park-switch/connector (which also kept playing up on the V8 until replaced) is also available from the parts houses.

    September 2008:

    Vee's wipers suddenly stopped working, moving about 1/4 the way across then stopping, and not parking or running at either speed. Fortunately I didn't need them as I had operated the wiper stalk instead of the indicator, otherwise it would probably have happened when I did need them! The fuse hadn't blown as the heater fan was still working. The electrical conditions at the (unplugged) harness connector seemed to be correct, so there was nothing for it but to remove the motor. Applying 12v and earth directly to the appropriate spades on the connector block got nothing out of the standard speed and just a brief movement out of the fast, then nothing, not even any sparking. So I opened it up, full story by clicking the thumbnail to the left.

    Brush Replacement May 2016: For a long time Bee's wipers have been reluctant to start moving, especially if not used for a long time like over winter. Sometimes I've had to switch to fast speed before they would get going properly, and after that they have continued to work back on normal speed. On our first run of the season I had to use them and they were even reluctant to start and keep going on the fast speed, so definitely time to investigate. We have a run in a few days where rain is expected again, so I decide to do something about it.

    The first thing I did was check the voltage reaching the motor, which to do properly one must do right on the connectors for the brush wires, which means taking the motor off to get at them. Remove the U-clamp securing the motor to the bulkhead, which makes access to the gearbox cover screws slightly easier.

    Take the cover off, slide the circlip off the large wheel crank pin, remove the shim under it, and remove the connecting rod that pushes and pulls the rack inner. Note another larger shim under the connecting rod. If you lift the blades off the glass, turn the wiper switch on, then turn the ignition on and off while watching the crank pin, you can position it to be lower down and so easier to access. Then the rack can be lifted out of the end of the gearbox, the motor unit lowered and turned over to unplug the harness connector. In theory you can undo the big nut where the rack joins the gearbox, and withdraw the motor complete with rack inner and so not have to fiddle with the connecting rod - if you can wield a large spanner that high up behind the dashboard. Many years ago that nut did work loose in torrential rain on a run, and I managed to reach up and hand-tighten it while still driving along, tightening it properly on our return home, but with all the extra wiring I have up there now I decided it would be easier to remove the con-rod as I did before.

    I poked some thin single-strand wire up the normal and fast connectors where the brush wires go onto the connector block, plugged the harness back, connected a meter to the wires, and switched on. Now this doesn't have the load of the wipers of course, but even so I'm only losing about half a volt, so the connections are OK. Next was to examine the brushes. Remove the two long screws that go through the motor case into the gearbox, and pull the motor unit off.

    It was immediately apparent that the brushes were very worn, even more so than when I had changed Vee's brushes when that stopped altogether. However it was only when reviewing this picture that I realised something else. Whilst the brush material itself is considerably longer on the unworn new item, the springs aren't pushing the back of the brushes anywhere near as far out as the old springs are. So unless they work out as they are used, only a small amount of wear will need to take place before these stop working properly as well.

    When fitting the new brush set make sure the blue wire is positioned between the screw boss and the side of the gearbox casing, and doesn't get trapped. It's the earth wire so shouldn't cause an electrical problem, but it will affect the alignment of the brushes.

    I took the opportunity to clean the commutator with white spirit, and draw a knife blade between the segments to clean them out.

    When refitting the motor, carefully hook the brushes back one by one so they fit over the end of the commutator ...

    ... and position the alignment marks correctly.

    With the motor casing screwed to the gearbox casing I plugged the harness in for an electrical test - and immediately found the same problem I had had with Vee's new brush set and that was the motor binding and running very slowly. Slackening the motor screws and tilting its case slightly freed the motor up, again exactly as before. This time determined to try and find the cause, I removed the motor case, refitted the old brush set, and refitted the motor, and it ran perfectly. Several times I had the motor off and on with both new and old brush sets and it always ran correctly with the old set, and always ran slowly with the new. The only point of contact between the brush set and the armature is between the brushes and the commutator, so there is no way they can be causing it when tilting the motor 'cures' it. It can't be the upper bearing in the gearbox casting as that is spherical externally in a spring mount so orientates itself to match the spindle. And it isn't the large screw in the gearbox casing that bears on the end of the armature spindle as I slackened that to give a clearance and it made no difference, and there is a nylon bush between the two anyway. It's a mystery, so again I resort to a washer inserted to create a gap on one side, i.e. tilting the motor relative to the gearbox. I reinstall everything, but may well investigate further when time and no imminent runs allow.

    Poor clearing: From time to time there are complaints on the various fora about poor clearing of the screen by the wipers - smearing and missed areas being the main ones. It's possible that people are comparing them with their modern cars, which is always a big mistake. It's also possible that people rarely use their MGBs in wet weather, so if they do get caught in a shower it's quite likely they are going to have dust, traffic film and flies, unless they are forever cleaning the screen before going out - and dust in particular is something I notice when taking one of them out after a break of a couple of weeks or so. After that it's down to arm and blade performance.

    I've done nothing special to either of mine but find particularly on the V8 that after the first few strokes after not being used for a long time the clearing is perfectly acceptable, and very similar to the ZS under similar circumstances. The roadster needs a bit longer perhaps, but again is perfectly acceptable. I have Smartscreen on both and use that far more than needing the wipers to be on constant, even in quite heavy rain, it just seems to bead and roll off, as if I was using Rain-X.

    Juddering is usually down to traffic film on either the screen or the blades, but can also be due to the 'angle of attack' of the blade to the glass. The blades work best if they can spread a microscopic layer of water across the glass as a lubricant, sweeping the rest away, a bit like when using a palette knife to ice a cake (you haven't lived ...). Lifted just off the glass the blade should be pointing straight at the glass, and movement in how the rubber is attached to the metal parts of the blade, and the shape and flexibility of the rubber tip, should allow the tip to lean first one way then the other as it sweeps across the glass. If the tip of the blade can't lean to perform a sweeping action and instead performs a chiselling action then it may well judder.

    The 'refill' i.e. the rubber and its steel backing should be free to move up and down through the pivoting parts of the arm. This enables it to follow the curve of the screen, and to move from a curved part to a flat part staying in contact with the glass. When mine are parked - right down on the rubber surround - only the very tip of the blade is not touching the glass, and only by a tiny amount. As soon as the blade starts it sweep it is fully in contact with the glass.

    The spring in the arm may be weak. After the first six months of production heavier 13oz arms were fitted.

    It's possible all the above may be correct, but the quality of the rubber (!) is just not good enough. From notes (which may be incomplete) Vee's came from Halfords in 2015, possibly Bosch, and Bee's have possibly been on since 1991! There are comments that 'Tex' blades are poor, but seem to be the ones most commonly stocked, NOS Trico being better. Googling shows Trico as currently available, quality unknown.

    Parking on the wrong side: November 2021

    • If you have just reinstalled the wiper rack/wheelboxes then check that the rack goes under the wheelboxes, not above, as here.
    • If you have just fitted a different motor then remove the cover when the wipers are parked and see where the crank-pin on the large gear is. It should have pushed the rack out of the gearbox housing, as here.
    • If it ha spulled the rack into the gearbox housing on the 14W 2-speed motor then the parking cam is probably in the wrong position, see here.
    • But if your wipers suddenly start parking on the wrong side when no work has been done, look here!

    Flying off: March 2020
    The arms should have some method of retaining them on the spindles. Mine have a spring-clip that hooks under the base of the splined section, and the blade has to be lifted off the glass to remove the tension between arm and spindle before I can remove them. If the splines are worn it may allow the arm to fly off when in use.

    Smartscreen Intermittent Control 

    RWTM Windscreen Wiper Timer Module

    The MG Owners Club and others sell a device called 'Smartscreen' which is eminently suitable for MGBs and Midgets at least and because the time delay is set using the standard wiper switch the device can be tucked away out of sight as it has no controls of its own. You use the existing switch on and off to start a 'learning' phase, then use the existing switch a second time on and off to terminate the learning phase, thereafter it repeats the delay until you turn the manual switch on for longer than one wipe or turn off the ignition. There is an enhanced version which operates the wipers briefly whenever the electric washers are used. I have the non-washer version and they are extremely useful, I find myself using intermittent far more than full-time, which saves wiper motor, blades and screen, as well as the switch when light rain/spray means you would otherwise need to keep turning them on and off (or flick-wipe) manually.

    Update January 2006: Apparently out of stock with the MGOC for a long time there have been rumours that they are available again. The suppliers web site is still online but there is no date information to indicate that it is still current, the contact page gives a phone number for enquiries. However Moss Europe show them with a price so maybe they are available again. Update August 2008: Allen Bachelder has commented on the MG Enthusiast BB that he ordered one from Moss (presumably UK as USA don't reference them) a couple of years ago but a different product arrived which uses its own control and so is not as neat as the Smartscreen system. Moss currently show the Smartscreen in the link above, so maybe you should check before you buy to see which you are getting.

    February 2013: I fitted the Smartscreen to Vee in 2001 and it has just packed up (lasted longer than many replacements for factory stuff) - the wipers start to run as soon as the ignition was turned on. I knew it was the Smartscreen and not the wiper switches as on this era the wipers are available with the key in the Accessories position, and they worked as they should, it was only when turned to Run before cranking that they started up, and I had powered Smartscreen from the ignition and not the accessories. After a bit of confusion - I got no confirmation web page or email or entry on my credit card, so thought the order had failed somehow and ordered again a week later. This time I got a confirmation email, but still no credit card entry or Smartscreen after a few days. Contacted the vendor who said he had received both orders so at least I was able to cancel the spurious one, and eventually it came another week later. Easy enough to swap the wires one by one and we are back working again. Always intrigued as to what's inside sealed boxes I opened it up to take a peek.

    RWTM Windscreen Wiper Timer Module August 2021
    There has been a question about connecting these on the MGOC forum. A less convenient device as it has its own rotary switch that has to be mounted somewhere, and only has five fixed intervals. Of the online instructions only one is directly applicable - earth-side switching for Mk1 roadsters - the rest vary to some degree. Mk1 GTs have a system that is only similar to Mk2 cars, Mk1 roadsters are completely different. Because the instructions are generic i.e. apply to lots of different marques and models they do not give any colours for the cars wiring, so you have to work that out for yourself. There is sufficient information on this site to work that out for the three (or four) options but I have added the colours to the Retronics drawings to make it easier.

    Wires and Terminal Numbering

    Wire Colours
    Wired Earths
    Joining (and adding) wires
    Wire Size and Current-carrying Capacity
    Terminal Numbering

      Wire Colours. The most important colours to remember are:

    • Brown - always live, unfused, feeds everything except the starter either directly or via the purple, white and green circuits
    • Purple - always live, fused (top fuse where there are two fuses, bottom where there are four), typically horns and interior lights
    • White - ignition, unfused, typically coil, fuel pump, overdrive
    • Green - ignition, fused (bottom fuse where there are two fuses, second one up where there are four), typically instruments, brake lights, reverse lights, indicators, wipers, washers and heater fan
    • Black - earth

    The following links display tables showing all the colours and wiring variations I am aware of and have been extracted from no less than 21 schematics in the Leyland Workshop Manual and Haynes and the 'changes by car and body number' tables in Clausager. I say 'all' but with the best will in the world I may have missed some or got some wrong, and there is less detailed information for the later variations than for earlier. The tables can only as good as the source material, and there are one or two where I suspect the published information may be wrong, but I have used them anyway.

    Note 1: The years are approximate, mostly coinciding with the model year changes which occurred from the start of MkII production in November 1967 i.e. at various points shortly before the end of the calendar year. As well as major changes at model year change points there were a succession of small changes throughout the year, these I have included as if they dated from the start of the model year.

    Note 2: 'North America' refers to the USA and Canada for all years plus Japan from September 1977. 'UK' refers to everywhere else. Note all LHD cars were to North American spec from 1977 on, and only roadsters were produced.

    Note 3: There are a number of cases where two electrically separate circuits appear to share the same colour wire at the same time, these I have denoted 'green/black 1' and 'green/black 2' e.g. in the case of the fuel tank sender to fuel gauge and heated rear window switch to the heated rear window in UK cars from 1968 to 1970. Other examples are the brown that goes to the hazards flasher via an in-line fuse and the green that goes to the indicator flasher via the hazards switch both of which should strictly speaking have changed colour. Some wires changed colour a number of times over the years like the wire from the starter relay to the solenoid: white/brown from 1970 to 1976, changing to brown/white for North American cars when white/brown was used for the ignition relay output, and white/red for UK cars with the ignition relay even though the wire from the ignition switch to the starter relay was already white/red!

    Note 4: The wire colours are listed in alphabetical order, main colour first, any tracer second.

    Note 5: 'Fuse' indicates which fuse, if any, protects the wire. In the case of the indicators wires this can either be the hazards fuse or the green fuse, depending on whether the hazards or the indicators are being used, there are other examples of this situation.

    Note 6: 'Component' indicates which items are connected together by the relevant wire, which may go through several bullet and multi-way connectors.


    1962 - 1964, all marketsGHN3-101 to 48756 Tourer only
    1964 - 1967, all marketsGHN3-48766 to 138800 Tourer,
    GHD3-71933 to 139823 GT
    1968 model year, UKGHN4-138801 to 158370 Tourer,
    GHD4-139824 to 158230 GT
    1968 model year, North AmericaGHN4-138401 to 158232 Tourer,
    GHD4-139472 to 158370 GT
    1969 model year, UKGHN4-158371 to 187169 Tourer,
    GHD4-158231 to 187840 GT
    1969 model year, North AmericaGHN4-158233 to 187169 Tourer,
    GHD4-158371 to 187840 GT
    1970 model year, UKGHN5-187170 to 219000 Tourer,
    GHD5-187841 to 219000 GT
    1970 model year, North AmericaGHN5-187170 to 219000 Tourer,
    GHD5-187841 to 219000 GT
    1971 model year, UKGHN5-219001 to 258000 Tourer,
    GHD5-219002 to 258003 GT
    1971 model year, North AmericaGHN5-219001 to 258000 Tourer,
    GHD5-219001 to 258003 GT
    1972 model year, UKGHN5-258001 to 294250 Tourer,
    GHD5-258004 to 296000 GT
    1972 model year, North America, without seat-belt warningGHN5-258001 to 276579 Tourer,
    GHD5-258004 to 268280 GT
    1972 model year, North America, with seat-belt warningGHN5-267580 to 294240 Tourer,
    GHD5-268281 to 296000 GT
    1973 model year, UKGHN5-294251 to 328100 Tourer,
    GHD5-296001 to 328800 GT
    1973 model year, North AmericaGHN5-294241 to 328100 Tourer,
    GHD5-296001 to 328800 GT
    1974 model year (chrome bumper), UKGHN5-328101 to 360300 Tourer,
    GHD5-328801 to 361000 GT
    1974 model year (chrome bumper), North AmericaGHN5-328101 to 360300 Tourer,
    GHD5-328801 to 361000 GT
    1974 1/2 (rubber bumper) - 1976, UKGHN5-360301 to 410000 Tourer,
    GHD5-361001 to 410350 GT
    1974 1/2 (rubber bumper) - 1976, North AmericaGHN5-360301 to 410000 Tourer,
    GHD5-361001 to 367803 GT
    1977 model year, UKGHN5-410001 to 447000 Tourer,
    GHD5-410351 to 447035 GT
    1977 model year on, North AmericaGHN5-410001 to 523002 Tourer
    1978 model year on, UKGHN5-447001 to 523001 Tourer,
    GHD5-447036 to 523002 GT

    V8G-D2D1-101 to 2903

     September 2010: See also this British Standard BS-AU7 listing of colour codes, sent to me by Stephen Strange and based on an original layout and format by Marcel Chichak, I believe. And this history of BS-AU7.

    Joining (and adding) wires: January 2020 Over the years wiring can deteriorate from heat and oil causing the insulation to harden, and crack with normal flexing, as well as from short-circuits and mechanical action causing more extensive damage. Short of replacing the complete harness it may be necessary to 'piece-out' or replace damaged sections. But first, a short section where the insulation has been damaged could be 'repaired' or at least protected with a length of heat-shrink to both strengthen the wire as well as cover exposed conductors. Getting the right size to slide over bullets is easy, less so where spade connectors are involved but still possible, although to fit over factory spades would need the rubber or plastic covers to be removed, and replaced with heat-shrink as well as over the damaged section. This method may not be adequate if any of the conductor strands have parted as that will reduce the current-carrying capacity of the wire.

    Where a section has to be replaced there are supplies of single and two-colour wire out there, although there are not many two-colour options available in 17 amp as there are in 8 amp, and that gauge won't be adequate for all circuits. To piece out, the existing wire will have to be traced back, possibly under the harness wrapping, to a sound section, then cut, stripped, and spliced with an appropriate length of new wire. There are very many ways of splicing - just Google 'hand splicing wires' or similar. Laying the two wires side by side and twisting the conductors will not get a neat result for piecing-out, it's only advantage is that you can fit heat-shrink after making the join if you forget to fit it beforehand! Splay the conductors out into at least two forks, partially interlace them, then twist the cut ends of each set of conductors around the base of the other wires conductors. This forms a good mechanical joint as well as electrical. The same techniques are used when adding circuits and wires.

    Soldering is the trickiest part. You need a soldering iron of sufficient power, and only hold it on long enough for the solder to flow into the joint. An under-powered iron will start damaging the insulation before the joint has got hot enough to flow the solder, and holding a higher powered iron on for too long will do the same. It should only take about a second for the right iron to flow the solder into the joint, and for automotive wiring you should need less than 1/4" of solder per joint. Never carry molten solder to a joint on the iron as per James May, the flux will have burnt off and it will not flow into the joint. If you have a good mechanical joint and the wire is self-supporting, or supported in some way, you only need two hands - one to hold the iron and the other to feed in the solder. Don't disturb the joint until the solder has solidified, this is usually visible as a slight change in appearance from 'silvery' to matt. If it goes a very dull grey you could have a 'dry' joint (the solder is not bridging conductor strands, the joint could move with vibration, oxidise, and develop a bad connection), either from a poor mechanical joint having moved as it solidifies, or the flux having burnt off for some reason. The conductors must be clean and bright or the solder will not flow, but stay in lumps on parts of the joint. Do not leave the iron on so long that the solder flows all the way through the joint and into the untwisted strands. When the joint has cooled slide a section of heat-shrink just slightly bigger than the joint over the joint, and apply heat to shrink it to typically half its diameter. A heat gun is best, blowing from both sides. You can use a soldering iron using the side of the heated tip, not the very end that you use for soldering or that may compromise the next joint you make.

    The other end of the wire will almost certainly go to a bullet or a spade connector.

    • For bullets strip only as much as is needed for the insulation to butt up against the back of the bullet, and the strands of the conductor to just poke through. Use a bullet with a hole in the end just big enough for all the strands to go through. Support the wire vertically so the bullet sits on it, wrap a piece of wet paper or cloth round the wire just at the base of the bullet, and touch iron and solder to the tip of the bullet, remove the solder as soon as some has melted, and leave the iron on just long enough to see the solder flow into the strands and onto the tip of the bullet. A bullet shouldn't need any heat-shrink unless you have overheated the insulation, or allowed solder to run down that far.
    • For spades use uninsulated connectors, or if they are crimp connectors use the type that only have insulation over the base tube where the wire goes, not over the spade. For non-crimp which are completely uninsulated there should be two pairs of tabs - one to fold down onto the conductors, and another to fold down onto the insulation for mechanical support. I only ever use crimp connectors, and never rely on crimp alone even using a ratchet crimp tool. There are those that talk about crimps being good enough for aerospace, and if you can get aerospace wire and crimps to fit our cars and a calibrated tool, then go for it. They claim soldering crimps will damage insulation and cause the wire to go stiff with solder and so make a weak point - and so it will if you use the wrong iron and/or use it for the wrong length of time. If the conductor strands are thin enough to fit into the spade when doubled, then I do. I also crimp in two places slightly apart, with the end of the conductors just visible at the base of the spade part. Again support the wire with the spade uppermost, and touch iron and solder to the tip of the conductors, remove the solder as soon as some has melted, and leave the iron on just long enough to see the solder flow into the strands and the connector tube. You will need a larger diameter heat-shrink to just fit over the spade, and long enough to extend at least 1/2" over the insulation, which will act as a strain-relief.
    The above information for bullets and spade connectors applies to adding wires for additional circuits of course, the attached shows this method used for male, female and piggy-back spade connectors.

    Wire Size and Current-carrying Capacity: December 2019 Wire gauge is often mentioned when people are asking what size they should use which seems to be the American way of specifying and leads to the abbreviation AWG (American Wire Gauge). In the UK it's more likely to be numbers of strands and cross-sectional area of each strand, which might seem more complicated, but a few strands of thick conductor won't be as flexible as many strands of thinner, and some wiring needs to be more flexible than others.

    The length of the wire also needs to be taken into account as all wiring has an inherent resistance which will cause a volt-drop, and thicker wire is needed for longer runs. This chart from shows what gauge should be used for various currents over various lengths, and this chart from AES converts AWG to diameter and cross-sectional area in mm. AES as well as specifying strands, conductor cross-sectional area and overall cross-sectional area also specifies its cable in terms of current (not taking length into account) and has 18 values in standard and thin-wall cable albeit in a very limited range of colours. Some suppliers have a wider range of colours including the tracer types used on the MGB, but the conductor size and hence current carrying capacity options may be limited.

    For battery and earth cables it's usual for the battery cable to be thicker than the earth for the same reason i.e. it is significantly longer. If replacing cables then keep to the same sizes as best you can, thicker is better especially for the battery cable, but bear in mind it will have to fit in the channels under the floor. I've used Halfords ready-made for short lengths for modifications in the past. The usual suspects i.e. MGB parts houses don't give any current or sizing information for off-the-shelf cables i.e. direct replacement but I think one can assume they are 'adequate'. AES sell battery cable by the metre, but you have add in terminals. And whilst attaching battery clamps to cable as easy enough the solenoid through-hole terminal is a different matter, needing crimping and/or soldering.

    Terminal Numbering.  Added January 2007 Very hit and miss with original MGB components as terminal numbering changed from time to time. In more recent years DIN (the German Institute for Standardisation) published Standard 72552 covering terminal numbering for pretty-well every electrical component in an automobile. The numbering seems to have been adopted world-wide and is most likely to crop up in connection with MGBs for additional and replacement relays, flasher units etc. Wikipedia DIN 72552 lists the numbers and their meaning, broken down into circuit areas, however 'Standard' is stretching the definition as several of the numbers have multiple applications.

    Wiring Harness Replacement

    Yes, 'HARNESS', not 'loom' as many call it.

    The terminology comes from weaving where 'loom' is machine that weaves the cloth. Alternate threads of yarn - the warp threads - are lifted up and the shuttle with the weft thread is passed under them, and above the remainder of the warp threads. Then those threads are lowered and the others raised and the shuttle passed back, so weaving the weft thread in and out of the warp threads. Each warp thread is lifted by a special wire with a loop in it, known as a 'heddle'. So there are many wires, the upper end of each of them being attached to one of at least two bars running the width of the loom. Each bar is called a HARNESS, and each HARNESS carries many WIRES. So there you have it - Harness, not loom.

    Note: For Mk1 cars all markets used the same main harness, designed to reach right across the car for LHD, turned back on itself behind the dash for RHD. For Mk2 and later cars even though there were separate North American harnesses this was more to do with additional circuitry for that market rather than differences between LHD and RHD, other LHD markets and the UK seem to have continued to use the same 'LHD' harness turned back for RHD cars. It wasn't until the 77 model year that all LHD roadsters conformed to the North American spec, at which point there was a RHD-only harness, a LHD for Canada, and another LHD for America and the rest of the LHD world. The V8 also had an RHD harness as it was never marketed in LHD form, even though seven were built for Federal testing in the USA, which probably had the North American dash, harness and everything else that market required.

    Split a length of thin cable sheathing or tubing up one side and put it over the edges of the two holes that go through the firewall to avoid damaging the harness tape or cloth as you work the new one through.

    Pull the old one back into the cabin and the new one from the cabin to the engine compartment.

    Tape the tails that come out of the new harness in the engine compartment to the thinnest part of the harness - some facing forwards and some backwards to end up with the minimum thickness. If you leave them free you will end up having to pull a greater thickness through the firewall than you need, and the later the model the bigger this problem becomes.

      The main, rear and gearbox harnesses joined together in more or less the same place, albeit lower on the 77 RHD and later with the long master cylinder and servo, and also for some reason on early cars when there was no similar space restriction. Interconnecting harnesses should be straight forward as in the vast majority of cases they are the same colour both sides of the bullet connector. Exceptions are the indicators where the tail from the light unit is green, whereas the harness wires will be green/white or green/red. Another is the 4-synch LH overdrive circuit prior to 1977 where yellow coming out of the main harness goes to yellow/red in the gearbox harness.

    In general spurs with their own harness wrap come out of the main harness adjacent to the component they feed which reduces the confusion of what goes where. After that the Autowire diagrams are going to be more helpful than the WSM or Haynes as to exactly which wires go to which component. On the original web site they only show up as full screen, but the ones linked here should allow you to expand them and be even clearer by clicking on it when you get the cursor with a + symbol in a magnifying glass.

    As time went by various sub assemblies connect to the main harness with multi-plugs which makes life easier, commencing with the indicator/dip/main/flasher switch, then the ignition switch and column wiper switch, and eventually the dash had it's own sub-harness with three (RHD) or two (others) multi-plugs for interconnection.

    Fusebox has brown wires on the lowest front spades and purple on the back. White on the next one up front and green on the back. for the 'four-fuse' fusebox red/green goes to either of the top two at the front and red on the back. Strictly speaking the red wires should be one fuse for one side and one for the other, they can be cross-connected between front and back, but it doesn't matter. The important thing if you've had the fusebox off is to fit it the right way up - the top two fuses are linked together at the front, which is why it doesn't matter which spade the red/green goes on.

    The ignition coil has a preferred connection with white on the SW or + terminal or two white/light-greens on the + terminal, and one or two white/blacks on the CB or - terminal.

    The earlier square wiper motor has separate spades and getting the connections the wrong way round can blow the fuse. The later 2-speed wiper motor is straightforward as that has a multi-plug and socket.

    The biggest problems are individual spades on things like the ignition switch and switches for the lighting and wipers, more info by clicking the links. Later rocker switches have multi-way connectors.

    Courtesy lights with manual switches such as for the GT load space also have to be connected the right way round or you will get a short-circuit when turning them on manually. The centre console courtesy light is connected using bullet connectors so as long as you match up the colours it should be fine.

    For dynamo and earlier 16AC alternator with the external control boxes/regulators terminals will be labelled. For later alternators multi-way plugs are used.

    Starter and ignition relay (where provided) should have marked terminals and the diagrams shows which wire goes where, ditto for solenoids and starters.

    The single-speed heater fan and overdrive switches and the later fuel and electric temp gauges only have two connections each so it doesn't matter which way round they go. The single-speed heater fan only has two connections but these do have to be round the right way as otherwise it blows very poorly. The 2-wire horns and the hydraulic brake light switch can also be connected either way round.

    The instrument voltage stabiliser only has two connections but those do have to be the right way round. Originally the arrangement of male and female spades meant that the wires would only connect one way, but more recent stabilisers may allow you to connect them either way round. In all cases they should have the terminals labelled B(attery) for the green wire with a female spade, and I(nstruments) for the light-green/green wire with a male spade.

    The later 2-terminal indicator flasher unit also has two connections labelled B(attery) for the green wire and L(amps) for the light-green/brown but can be connected either way round, as with the hazard flasher.

    For any additional wiring (for which you may not have any diagrams) make absolutely sure you have very detailed notes or pictures, or cut them taking a little bit of the original harness, so you know where it all has to go back to.

    Bullets are only crimped on, unlike the spades which are spot-welded, and can pull off as well as corrode internally. With all the lighting bullets at the front of the car drill a conical depression in the end so it shows both shiny brass from the bullet and shiny copper from the wire, and fill the depression with solder making sure you get the bullet hot enough for the solder to run, but not so hot as to damage the insulation. A high-power iron used briefly is best. Make sure the outside of the bullet is clean (no flux) and shiny after soldering. Do this to the old wires from the lights too.

    Use all new bullet connectors (particularly at the front) and put Vaseline inside them and on the bullets before assembling which makes them easy to assemble as well as protecting against moisture. Make sure both bullets are pushed home inside the connector, and ends of bullets or the end of the metal connector are not poking out of the insulating sleeve.

    When reassembling the multi-plugs for the column switches and the later dash make sure all of the pins are pushed fully home, and not pushed partly out the back of the connector so only the tips are touching.

    Note: On rewiring a UK 1980 I had some really curious issues with the fused ignition i.e. green circuit components, until I discovered that the two additional in-line fuses for some of these circuits (under the fusebox) had been cross-connected i.e. brown to brown and green to green. Reversing these corrected the problem. This had come about because one circuit has the brown coming from the front and the green going towards the rear, and the other circuit the other way round, but both circuits had the fuse holders installed in the same orientation instead of one facing one way and the other facing the other way. Had both fuse holders been connected with the short cap on the brown and the main body on the green, for example, it wouldn't have been possible. Murphy's Law - if something can be fitted more than one way but only one way is right, someone somewhere will eventually fit it the wrong way.

    The body/boot harness can be a real pain, unless damaged leave it alone. The mass of bullets form a diameter greater than the some of the support brackets, and whilst you will be able to get some of the bullets through in one go you will have to thread the remainder through one at a time. However on 67 and later cars with the solenoid on the starter, unless you can remove the fixing nuts for the brackets down the inner wing (a real challenge with a V8, even more to replace them) you may have to remove the body harness in order to get the thick wires that go to the starter together with their big lugs through the brackets first. In the case of a 1980 with a V8 conversion I had to tape up the end of the body harness, with the bullets slightly staggered to reduce the maximum width, then I could pull it through from above using a pulling wire also taped on.

    The main rear and chrome bumper front parking/flasher lighting units do not have earth wires but rely on the mechanical fixings. Consider adding earth wires from a fixing screw. Later cars should have bullet connecters nearby, early cars will have to go back to the number-plate fixing bolt earthing point.

    If you have any additional wiring do not rely on crimp connections alone, they simply are not good enough. Get the semi-insulated spade terminals that allow you to solder after crimping, using heat-shrink to cover the whole connector afterwards. Do not use those tubular crimp wire extenders as they cannot be soldered at all. Use a male and a female spade, soldered as well as crimped, assemble with Vaseline and put heat-shrink over the lot. Crimp-type bullets do not fit the original bullet connectors without distorting them.

    Clean up all the body earth points and use Vaseline when bolting the earth wires to them.

      Before reconnecting the battery for the first time make sure everything else is connected as you think it should be, and turn everything off, including any interior and boot/trunk lights, clocks, radio etc. Connect the thick starter cable to the battery but not the earth strap. Connect a meter set to display 12v between the battery earth post and the car body. If it shows 12v then some circuit is drawing power (if you have an alternator you should see a few volts, this is OK). I also have an old headlamp bulb with two flying leads, if this lights up at full brightness when used in place of the meter you have a full short to earth from somewhere. Don't reconnect the battery earth strap until you are sure there are no shorts. Start with everything switched off, and the bulb should be out. Then switch each circuit on in turn, one at a time, and the test bulb should glow to some extent. You should be able to test everything except turning the ignition key to the crank position. The more powerful the circuit being tested, the brighter the test bulb will glow. The brighter it is glowing, the higher the voltage will be across the test bulb, and the lower it will be across the circuit being tested. This means that low-current circuits may well appear to be working normally, but higher current circuits will only work weakly or not at all. Turning on headlights (the next highest current circuit after the starter) will make the test bulb glow pretty brightly, but there should still be some glow from the parking lamps at least. If you do happen to turn the key to the crank position, the test bulb will glow at full brilliance, as the solenoid takes a very high current, and it won't operate. In fact if you have a starter relay, you will probably find this chatters and the test bulb flickers. This is because there is enough current through the test bulb to operate the relay, but as soon as the relay contacts close, and connect the high-current circuit of the solenoid to the battery, the test bulb glows brightly, which means it is taking all the voltage. There will be little or none left to keep the relay operated, which will release. As its contacts open the current will drop, meaning that the test bulb dims, the voltage available for the relay goes up again, so it operates again, and so on.

    Won't Start

    This could mean several things like:

    "It isn't turning over when I turn the key" or
    "The solenoid is chattering" or
    "It spins the starter but not the engine" or
    "It cranks very slowly" or
    "It turns over normally but won't fire" or
    "It fires occasionally but not enough to run" or
    "It only fires up as I release the ignition key" or
    "It starts but cuts out again when I release the ignition key" etc.

    On the other hand, you could have the "It starts cranking as soon as I turn the ignition on and won't stop until I release the handbrake or disconnect the battery!!" problem.

    The diagnostics below relate to points and coil systems, not electronic systems either factory or aftermarket.

      "It isn't turning over when I turn the key"

    Circuit chain: battery - heavy current circuit - brown circuit - ignition switch - white/red circuit - starter relay (inner wing) - white/brown circuit - solenoid - starter body - engine - engine earth strap - body - battery. Click the link for starter schematics .

    Note 1: Until some point in 1969 the white/red went direct to the solenoid, even when the alternator and pre-engaged starter was fitted. After that the relay was fitted.

    Note 2: Updated May 2006 Note that on the V8 there is an insulated stud mounted under the RHS toe-board by the chassis member where the browns, long cable back to the battery, and a short cable forward to the starter motor, all join together, which is an additional point where bad connections can develop.

    If you normally have the ignition light glowing between turning on the ignition and starting the car, is it on now?

    No - check battery, heavy current cable, brown circuit to ignition switch, white circuit from ignition switch. Click the link for starter schematics .

    Yes - does it go out or nearly out when you turn the key to the start position?

    Yes - could be insufficient charge in the battery (check by putting a known fully charged battery on the car) or bad connections in the heavy current cables and engine earth strap, check these with this method. It could also be the starter jammed in mesh with the flywheel. This usually only affects inertia starters i.e. those with a remote solenoid. Try putting the car into 4th and rocking it back and fore to free it.

    No - can you hear a clicking when you turn the key to the start position?

    No - is there 12v on the white/red wire at the ignition switch? No - possible faulty ignition switch.

    Yes - is there 12v on the red/white terminal of the starter relay and earth on the black terminal?

    Yes - possible faulty relay winding or contacts jammed open.
    No - check white/red and earth wiring at ignition switch and relay.

    Yes - is it the relay or the solenoid?

    Relay only - check that 12v is coming out of the relay onto the white/brown wire and getting to the solenoid terminal. If it is, possible faulty solenoid otherwise possible faulty relay contacts or wiring between them.

    Solenoid - possible bad contacts on solenoid, or brushes/windings on starter motor, or connections between solenoid and starter (some pre-engaged starters have the connection from the solenoid to the starter exposed, check here as well).

      "The solenoid is chattering"

    Is the engine turning? No - either the battery is flat or there is a bad connection in the heavy current circuit. Continue as for "It isn't turning over when I turn the key".

    Yes - probable bad connection in the solenoid operate circuit. With the key turned to 'start' check the voltage on brown and white/brown connections at the starter relay, and at the white/brown spade on the solenoid. Any sudden voltage drops indicate a bad connection. If the voltage on the relay brown spade is good but on the white/brown spade is low then the relay is bad. If you still have 9v or so at the white/brown spade on the solenoid then the solenoid/starter is suspect.

      "It spins the starter but not the engine"

    This usually only affects inertia starters (i.e. remote solenoid) and can be caused by a dirty or sticky pinion. This pinion is on a spiral 'thread' with a very coarse pitch. When the starter starts to spin it tries to spin the pinion, but the 'inertia' of the pinion and the direction of the spiral means that it slides up the spiral into engagement with the flywheel, and only then starts turning. If this spiral is dirty the pinion doesn't move into engagement with the flywheel, it just spins where it is. Most books tell you not to oil the pinion and spiral, and it is true that oil will hold dirt and cause the problem. But I have also found that a 'too clean' pinion and spiral will also stick. After several bouts of 'remove, clean, refit, wait, stick' many years ago an old hand told me to put a drop (literally) of oil on the pinion and after that the problem never came back.

      "It cranks very slowly"

    Could be insufficient charge in the battery, or bad connections. The first check is to look at the ignition warning light, or turn the headlights on, then crank. If the lights dim right down then either the battery is flat, or its connections or the battery cable connection to the starter is bad. Check by putting a known fully charged battery on the car, and check the connections as described here. Note that V8s have an additional connection in the battery cable under the driver's toe-board. If the lights stay bright then the problem may be in the starter or solenoid.

    Update December 2008: Brian Smith on the Bulletin Board had this problem and mentioned his ignition warning light dimmed significantly while cranking. It suddenly struck me that as well as indicating a low battery or bad connections at the battery or solenoid, it will do the same if the engine/gearbox earth strap is bad as well. How does that get us any further forward? Well, the ignition warning light gets its earth from the engine when it isn't running, but all the other lights on the car get their earths from the body. So if, say, the interior light doesn't dim at all or only very slightly during cranking when the warning light dims a lot, that is probably an indication of a bad engine earth strap, and that was indeed what was happening on Brian's car, jumping from another battery and cleaning up the battery earths having had no effect. Connecting a voltmeter between the engine (+ve probe) and a known good body earth (-ve probe) would reveal this by showing some voltage during cranking. Ideally it should only show 1 or 2 tenths of a volt, if it shows any more it is probably worth cleaning up the engine earth strap, and this did the job on Brian's car.

      "It fires occasionally but not enough to run", and "It only fires up as I release the key"

    Do you get a good and regular spark at each plug lead? No - follow "It turns over but won't fire" above.

    Yes - check fuel delivery and carbs; check timing and order of leads from dizzie to plugs.

    September 2019: A pal with a TR4 spluttered to a halt shortly after leaving home having not used the car for a while. Since then it would make an occasional cough then cut out, but only as he released the key while cranking, which apparently was what normally happened. He said the spark looked weak so with that and only trying to fire as he released the key suggested a bad condenser. Tried one of my known good spares from the points wire on the coil to earth but no different. Checked the plugs and the front pair were soaked, the back pair less so. Peering in the carb intakes while cranking I could see fuel pulsing up the jet, so flooding, i.e. float valve stuck open. These are Strombergs with no overflow pipe to the floor and engine-driven pump so no clicking. That fixed, the spark was still weak, but also intermittent. Checked the points volt-drop and that showed they were high-resistance so cleaned them, but other than that they were opening and closing as they should. Maybe a bit better spark but still intermittent, then no spark at all. Check the coil and the secondary had gone open-circuit. Fitted my spare coil and spark again, but still intermittent. Checked the HT leads and two were open-circuit - silicon cores not trapped under the crimp in the plug caps - new cap and leads to be obtained but in the meantime I fit my cap and leads. Spark now better but still intermittent. A couple of days later fitted his new cap and leads, and new rotor, but still intermittent sparking, confirmed from two Colortunes and a timing light on a third plug lead. By now I'm beginning to tear what's left of my hair, and pal says to fit new points and condenser which he'd got at the same time as the other stuff, from Powerspark. The first problem with those was that the condenser and spade connections had been attached to the points incorrectly so the tags and leads would have been trapped under the cap, and the condenser didn't reach its slot on the points plate. Corrected that, but couldn't close the gap enough as the end of the points spring was sticking out and pressed against the fixing screw - shorting the points out! After bending that out of the way, and discarding the large washer that had been under a spring washer and looked to me like it was also up against the points spring, the screw still looked very close to the spring. So I slackened the nut and pressed the spring out of the way and retightened the nut. Finally we could adjust the new points! Switched on, cranked, and it burst into life - and before he had released the key, and did so several times! On a test drive pal said it was going better than it ever had before. I reckon it was a weak spark originally from the two bad leads, which was causing it to only fire as he released the key and the ignition voltage went back up, also causing the HT voltage to rise much higher than normal as it struggled to jump the increased gaps, which sapped power, and eventually took the coil. The float valve was probably because of a period of idleness, and caused the initial problem. When first looking for the problem pal had reset the points gap which I reckon had put the points screw or washer too close to the points spring, and the 200v or so that appears across the points was enough to jump that gap, which killed the spark. Comparing with mine after the event I'm sure his screw has a larger head, but presumably the same thread, and the washer was definitely bigger than mine.

      "It starts but cuts out again when I release the ignition key"

    This problem usually only affects cars equipped with a 6v coil and an external ballast resistor. The coil normally runs at 6v and is fed from the white circuit via the ballast resistor, usually a length of resistance wire contained within the harness with a white wire at the ignition switch end and a white/light-green at the coil end. The coil is boosted to 12v during cranking by the white/light-green circuit from the solenoid which effectively bypasses the ballast resistor. The fault is caused by a disconnection somewhere in the white circuit - ballast resistor - white/light-green circuit - coil chain. Click the link for ignition schematics .

      "It starts cranking as soon as I turn the ignition on and won't stop until I release the handbrake or disconnect the battery!!"

    This problem affects late-model cars to both North American and UK spec and is caused by the brake-warning diode going short-circuit. More information here.

      Won't Switch Off!!

    For North American spec cars with the ignition relay i.e. 1977 on, where the ignition warning light is working normally, and the engine runs normally when the ignition is turned off, see here. In all other cases where the engine continues to run normally see here. For the rocking and rolling Dieseling-type run-on see here.