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

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The sectioned MGB at the British Motor Museum, Gaydon

Indicator/turn signals and hazard flashers

Indicator/turn signal schematics
Hazard warning schematics
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

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 or turn flasher units (they are not relays, strictly speaking they are 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 (originally ATJ8880, Lucas 9FL) with the third pin flashing an additional hazard tell-tale lamp even though the indicator/turn signal repeaters are also flashing. From 1972 the additional tell-tale seems to have been connected to the hazard switch instead, and a 2-pin hazard flasher unit is shown. However V8s have the same part number listed but 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 unit available at the time, identical to the original MGB indicator unit, so perhaps that is where the confusion on the diagram stems from.

Several suppliers are showing SFB115, GFU2124 and GFU2125 as the replacement for ATJ8880, but images show these are capable of operating only two 21w bulbs i.e. they are indicator units, not hazard units capable of flashing four 21w bulbs. The correct item is SFB130, aka 35053.


Fault diagnosis -
Indicators/turn signals

  Indicators/turn signals: Updated July 2015: From 1962-67 a cylindrical 3-terminal flasher unit was used, but 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, not realising that the bad connections are 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. Fitting an electronic flasher unit only gets round the 'slow flashing' problem - probably bad connections somewhere along the line - temporarily. Eventually you may have to find and fix the root cause, you might as well do it now and get brighter lights. 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 ignorant of the fact 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 - heavy current cable - brown circuit - ignition switch - white circuit (note 1) - No. 2 fuse - green circuit - hazard flasher switch (note 2) - green circuit (note 3) - turn flasher - light-green/brown circuit - turn flasher switch - green/white (RH side) and green/red circuits (LH side) - turn lamp holder - turn lamp - turn lamp holder - black circuit - earth - battery.

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

Note 2: The turn 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 turn flashers from conflicting with each other, but more importantly prevents the hazards feeding power back through the turn switch, turn 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 turn signal problems.

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

Typical turn signal 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 turn 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 turn flasher to the turn 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 turn 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 turn signal 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 turn 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.

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 turn 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.

  LED flashers Updated March 2015 Many new cars these days are being fitted with LED ancillary (i.e. other than headlights) lighting including turn 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, they are not legal for use on public roads, only off-road or at shows. 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 also get an indicator flasher unit specifically for LED lamps which will flash them at the correct rate - 2-pin with a red case. But again, these do not tell you when a corner has failed and so are as equally unsafe as load resistors with standard flashers or the so-called 'heavy duty' types, and if you should connect more than one incandescent bulb to them you will burn them out. The supplier 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 their 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 CANBus on modern cars should detect disconnections in the wiring right up to the bulb holder, but still can't detect failure of the light emitting part, and they do fail, especially after-market components.

Note that if you fit LED lamps and the LED indicator flasher unit you will need to change the hazard flasher as well. Whilst hazard flashers can 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 is far less than one incandescent (21 watts i.e. 1.75 amps).

  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 hazards 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 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 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 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 turn 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 turn signal 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.

  Indicator/Turn Switch Updated December 2009

Indicator/turnswitch and Cancelling Striker Positioning

For cancelling, early cars had a peg screwed into the column, later 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. 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.

Click on the thumbnail for a general view of the 62-68 switch and details of switching and cancelling from a 73 roadster, which was similar to that used up to the start of the 77 model year.

Note that the clip-type cancelling cam or striker changed twice - once in June 73 from BHH254 to BHH1301, and again in September 74 with the change to rubber bumpers to BHH402. It's not immediately obvious why as the column doesn't seem to have changed at either of those that points, and although the switch changed for rubber bumpers it didn't 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. That is one of non-cancelling, and 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 and striker (not changed by me at any rate) has never been a problem. One of these days I'll get both cowls off and compare them.

  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.


Main lights
Uprated Headlamps - Relays and Fuses
LED park/stop/tail lights
Headlamp Flasher
Headlamp Adjustment
Headlamp Mounting
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
'Lights on' warning buzzer
Switch Illumination
Daytime Running Lights (DRLs)

Main lights:

Parking lights (70-on)

LED park/stop/tail lights

Both front and rear parking/brake/indicator light clusters rely on the physical fixings to the wings to pick up an earth/ground. 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. The headlights do have a wired earth/ground, to a bolt near the right-hand headlight on early cars, moved to near the fusebox on later cars (probably Mk2). Originally unfused, from 1967 to 1969 the front and rear parking lights were separately fused using in-line fuses, one fuse for the front and one for the back.

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 harness bullets by the headlights. The harness probably changed to have a group of bullets by each headlight with the Mk2 in 1969 or for the 1970 model year, when cars got twin horns in North America (1969) and elsewhere (1970).

As can be seen the parking lights were not fused originally. Mark II cars introduced fuses, although the front were on one fuse and the rears on another, so if you had a short you lost both at one end, a particular problem at the rear as you would lose both tail and both number plate lights. The fuses were of the in-line type, probably where the rear harness joined the main harness near the fusebox, for just two years.

Parking lights 70-on:

For the 1970 model year a four-fuse fusebox was provided, the additional two fuses (at the top) being for the front and rear parking lights. This had the much better arrangement of one fuse feeding each side, so in the event of a short and a fuse blowing you still had one front, one rear, and the number plate light/s on one side still working. There is only one wire (red/green) feeding the parking light fuses, so they are linked at the front, which means if refitting a fusebox you must be careful to fit it the right way up, or you can get the purple circuit linked to the green and white circuits, i.e. effectively powering the ignition all the time.

All rear light clusters, and the front parking/indicator clusters on chrome bumper cars, rely on the physical fixings to the wings to pick up an earth/ground. 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. The headlights do have a wired earth/ground (also used for rubber bumper parking and indicator and North American side markers), to a bolt near the fusebox. This arrangement fuses each side of the car (not headlamps) independently via the top two fuses in the four-way fuse block. If one side is out 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.

On these cars the main harness has several bullets for the right hand lights and a tail for the right-hand horn breaking out by the right hand headlight, and the harness continues across the slam panel to the left hand headlight for the lights and horns there. One disadvantage of this arrangement is that the main and dipped beams and the parking lights 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.

LED park/stop/tail lights: October 2015

As with LED indicators these may not be legal as a retro-fit. And although LED front parking lights probably will be brighter and whiter than the originals the stop/tail versions can be very variable. A pal fitted them front and rear a while ago but they have failed an MOT by being 'adversely affected by the operation of other lamps' aka 'Discoing'. When the indicators (incandescent in this case) were going one side there was a very clear effect on the front lights and the tail and the stop lights on the other side. Three effects - one was visible slight dimming of the tail or stop lights while the indicators were lit, but the other was a very apparent momentary additional dimming of the tail or stop light at the instant the indicator bulbs were powered. This momentary dimming was also apparent every time the fuel pump clicked, although that is less of an issue. But the biggest problem was that when the brighter brake lights were already lit, turning on the parking lights dimmed the brake down to tail light level, and if the tail lights were already on powering the brake lights did not increase the brightness at all - totally unfit for purpose. A second set of a different type from another source had didn't do that but had their own problems.

  This second set did not have the major defect of the stop lights not working when the tail lights were on, but to 'compensate' (I jest) for that they had their own major defect if you should happen to get a short-circuit on the stop-light wiring. This would blow the green circuit fuse as expected, but it also completely extinguishes the tail lights! Both these major defects are almost certainly due to the way the LEDs are wired inside the plug-in unit. LEDs need a resistor in series to limit the current and reduce the voltage down to the 2v that each element typically needs, and in both sets this has obviously been done in such a way - even though the two sets differed - to cause these unwanted interactions between stop and tail.

But even when everything is working 'normally' the second set are not all they are cracked up to be regarding brightness. Neither tail nor stop are any brighter than tungsten, with stop noticeably dimmer in a side-by-side comparison with a tungsten bulb that is at least 26 years old. But the biggest difference is the greatly reduced radial output, as can be seen in the images.

Other people have found that although some versions do have brighter tail lights than tungsten, the stops were much the same, which means there is less of a step change from tail to stop. I can remember this complaint from when I first started reading about LEDs in MGBs quite a few years ago now. As this makes the stop lights easier to miss unless a following driver is looking towards the back of the car, which has to be balanced with LEDs coming up to full brightness noticeably quicker than tungsten, although later MGBs with the pedal-operated brake light switch come on very significantly quicker (except when panic-braking) than hydraulic switches. With all the other problems, my pal refitted tungsten and gave the whole idea up as a bad job. See also these comments: Video 1, Video 2, Alfa forum and Land Rover forum legal opinion.

But back to the first set and the 'discoing'. The first thought was bad earths or other connections even though when incandescent bulbs were substituted these effects were barely noticeable - had it been bad connections incandescent bulbs should have been much worse as they are much more sensitive to even small amounts of unwanted resistance. Also some time later these lights were fitted to another car and had the same problems. Despite that, some time was spent measuring voltage and volt-drops through the ignition and lighting circuits. But comparing with my car with incandescent bulbs at the corners of the car there was nothing out of the ordinary, which confirmed the suspicion that it was nothing to do with bad connections. However I also noticed on my car that when I turned on any incandescent lights, or the fuel pump clicked, the LED DRLs also appeared to dim momentarily. This got me thinking, and I have come to the conclusion that although the very low current consumption of LEDs makes them relatively insensitive to resistance from bad connections, they are at least as sensitive to voltage changes as incandescents, and probably more so.

Let me explain. A given resistance in series with an incandescent bulb on the one hand, and an LED on the other, is going to have a much greater visible effect on the light output from the incandescent than it is from the LED. This is because the higher current of the incandescent will cause more voltage to be 'lost' across the additional resistance than the low current of the LED will, therefore there is going to be significantly less voltage left for the incandescent than there is for the LED. But, if you reduce the voltage to both bulbs by the same amount, even a small amount, they both visibly dim.

Secondly even the best of circuits, and especially our 40 year-old classics with the connector technology of the day, will have very small but finite resistances at each connection point throughout the circuit, each 'losing' it's own little bit of voltage. Where these are lost in parts of the circuit common to two or more bulbs, i.e. indicators and brake lights, turning the indicators on will slightly reduce the voltage going to the brake lights, and vice-versa, hence reducing the current flowing through them, hence reducing their brightness. This is why, with the original type of indicator flasher unit, your flashers probably slow down slightly when you apply the brakes. However this was not the cause of the problem.

There is another significant difference between incandescent and LED lamps: Incandescent lamps have a filament that has to heat up when they are switched on, and the resistance of the filament varies very significantly between cold and hot, being very low when cold, and relatively high when hot. In the case of a pair of 21w bulbs as used for indicators and stop lights for example, they will draw about 3.5 amps when glowing, which implies a resistance of 3.4 ohms. However if you measure the resistance when cold you will see only a few tenths of an ohm. When 12v is first applied to these cold bulbs, they will try to draw 40 or more amps. You might think that would be enough to blow the fuse and you would be right - if that was the steady-state current. But just like bulbs, our fuses have to heat up and melt before they can blow. And as soon as any current starts flowing in the bulb filaments they heat up quicker than a fuse, so their resistance rapidly starts going up, which rapidly reduces the current through the fuse to its 'normal' level. But at the instant voltage is applied to the bulbs, the many various very small contact resistances all through the circuit mentioned above lose a significant amount of voltage going to those bulbs, both incandescents and LEDs. This drop in voltage affects everything else fed by that circuit, including tungsten bulbs and LEDs that are already lit. However whilst you will see a momentary flicker in the LEDs, you will not on a tungsten bulb as it takes time for it to 'cool down', and before it has done so enough to be visible the voltage has gone back up again. You will not see this voltage dip on a meter either as it is so brief - you need an oscilloscope. I do happen to have one - albeit very old and not of the highest quality, but even on that the dip in voltage is of the order of 4 volts or so for about 5 milli-seconds. By contrast LED bulbs take the same very low current when they are initially powered as subsequently. This means that turning on LED lamps doesn't produce a momentary current surge and consequent loss of voltage, and hence has no visible effect on other lamps - either incandescent or LED.

There is a third difference between incandescent bulbs and LEDs: As explained above incandescent lamps have a filament that has to heat up when they are switched on, and that takes a visibly finite time. Likewise when they are turned off they have to cool down, and again that takes a visibly finite time. By contrast, LEDs are at full brightness the instant they are powered, and extinguish the instant power is disconnected. This difference is very easily seen on cars with an LED third brake light but incandescent stop lights, as the third light coming on quicker and going off quicker, even though both types are powered from the same switch. And this brings us to the main reason why said pal's car failed it's MOT.

Because he was using incandescent indicator bulbs, but LED stop and tail, all the effects of the differences between the two types came into play. The momentary but very high current pulse when first powering the incandescent indicators each time they came on, and the resultant momentary but significant reduction in the supply voltage (3v in my tests), was clearly visible on the LED stop and tail lights. When incandescent bulbs are fitted all round, because the stop and tail filaments take a finite time to dim, this momentary voltage reduction (a few milli-seconds in my tests) is barely visible. You can see the same effect on incandescent lamps when cranking, as even though the voltage drop is less (typically from 12v to 10v with a good battery) the reduced voltage occurs for significantly longer each time a piston is rising on its compression stroke, long enough for an incandescent lamp to visibly dim. But that effect is, of course, not a problem in normal use.

All this explains the very brief but significant dimming of the LED stop and tail lights (and DRLs) each time the indicators light up, but what about the visible dimming of the stop lights when the parking lights were turned on?

If you look at incandescent stop and tail bulbs they actually brighten very slightly when you switch on the parking lights with the brake lights already illuminated, as you have an additional filament being powered and glowing, albeit only 5w in addition to the already glowing 21w. If you look at a typical stop and tail LED unit and power first the tail contact, you may well find that all the LED elements light up - not perhaps what you might expect. Now take the power off the tail contact and apply it to the stop contact, and again you see all the elements light up, but this time brighter. That is deliberate as it results in the greatest illuminated surface area in each case, which gives better visibility than having one section illuminated for tails and another section for stops. It is achieved by having different resistors from each lamp contact to the LED elements - a higher value resistor giving the lower level of brightness for the tail lights compared to the stop lights. So now we have the situation that once the stop lights are powering all the LED elements brightly, when additionally powering the tail contact nothing should happen. And if you test the LED unit away from the car with a separate voltage supply, that is probably what you will see. So why do you see a difference when it is fitted to the car? Probably because quite a few other lamps are switched on with the parking lights, and taking current, and in the case of the car in question this included four 5w incandescent number plate lights. And why isn't this effect as visible on incandescent stop and tail lights? Probably because the additional filament being powered by the tail lights is masking the overall slight reduction in supply voltage caused by the additional load.

And what about when the fuel pump causes a similar dimming? That just involves applying power to a solenoid, which doesn't have the cold inrush current of incandescent bulbs. In fact a solenoid (like an ignition coil) is effectively an inductance, and one of the properties of an inductor is that it tends to oppose the current and delay its rise to a peak value i.e. the opposite of the inrush current in a cold bulb. However the solenoid on a pump measures about 2 ohms, giving a current of 6 amps at 12v, which is near double that of a pair of indicators. And looking at that on the scope although the duration of the reduction in voltage is quite a bit less than when the indicators are going, the voltage itself reduces by much more, at 6 or 7 volts, i.e. momentarily the 12v supply has dropped to 5 or 6v!

If you had LED lamps everywhere - indicators, number plate lights, instruments as well as all four corners of the car you may well not see these effects (apart from the pump). But LED indicators have a significant safety issue as described here. Ironically these dimming and brightening effects could be 'designed out' of LED units, but it would increase the cost so is probably why it isn't done. As stated above all LEDs need a series resistor to operate off 12v, as each LED element has a limit of typically 2v. A series resistor is a cheap way of doing this, but as shown it does mean that any change in supply voltage causes the light output to change. But if a voltage regulator of, say 5v was fitted internally, together with a different resistor to reduce 5v to 2v instead of 12v to 2v, then the LED unit would be able to ignore these changes in the system voltage. As long as the supply voltage remained above 5v, the light output would remain constant. But as I say, there is a cost implication, and these days (for utility items anyway) price is everything.


The column mounted dip-switch can be a bit difficult to puzzle out as it incorporates a headlamp flasher, indicator/turn signal, and 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.

    Headlamp Adjustment:

    First, remove your trim-ring! With the possible exception of later models these can be a right pain. So much so, that 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 (or remove them yourself beforehand) until successfully passing the headlamp alignment test in the MOT, or taking it for alignment before fitting them. 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 I seem to recall having seen some rings with notches that allow you to reach the two adjustment screws with the rings in-situ.

    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. However 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 a sight 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 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! At the same time, pressing down hard on the top of the ring with the other hand can help. This should ease the bottom of the ring forward enough for you to 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 the rear edge of the ring, which is turned over to face forwards. This means that instead of the clip sliding off the ring as the ring is eased forwards, it would have to be bent right forwards, severely distorting it. With the bottom pulled forwards this far I did then try levering the bottom of the ring upwards to get the top of the ring unhooked from the two lips at the top. I could get the one 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. 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, but it had 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.

    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:

    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, although the parking/rear/side-marker lights were from 1967, firstly by a pair of in-line fuses one per end, then from 1969 by the top two fuses in the four-position fusebox one per side. Because you are adding wiring it does make sense to fuse it, but simply providing one main fuse could result in the total loss of headlamps if it should fail, so think in terms of providing one fuse 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 them close to the point at which you pick up the supply 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 15amps per filament, which is about double the typical current flow, and 30amps minimum for the main fuse.

    Click on the link for the schematic and suggested layout. The standard wiring has two double bullet connectors by the right-hand headlight. Position the filament fuses close to the relays, a four-way blade-type unit is ideal. 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.

    Daytime Running Lights (DRLs):

    Ubiquitous now, and getting so bright there has to be a risk that cars without could be missed. 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!

    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 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. Read the descriptions and look at the images carefully - compare the overall and thread sizes, this supplier was the only one I could find 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 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


    As factory wired. Replacement hydraulic (at least) switches 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, and subsequent replacement no better.


    RHD chrome bumper cars use a hydraulically operated switch in the junction on the inner wing near the fusebox. Rubber bumper cars up to September 76 use a mechanical switch mounted on the front of the pedal box. Up to now these cars have had a single-circuit braking system, with or without a remote servo. For the 1977 model year a combined master and servo and a dual-circuit braking system was fitted, with the brake switch on a bracket in front of the pedal in the cabin.

    North American cars originally had the single-circuit system with the hydraulic switch, but for the Mk2 in 1967 had a dual-circuit system - unboosted - with the switch on the front of the pedal box. For the 1975 model year they got a boosted dual-circuit system, with a combined master and servo, and the switch was at the back of the pedal box, where access is quite restricted.

    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 master.

    The mechanical switch needed to move when the combined master and servo was fitted as the 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 pivot. Why the switch on American cars is in restricted space in the engine compartment whereas the RHD switch was in the cabin isn't known. 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. However 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 a bit of an 'early warning' of braking which is a safety feature. The hydraulic type are not adjustable, but the mechanical type are 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 the brake lights come on, and it is only when the pedal is released and operates the switch that 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 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 box, master push-rod and all sorts.

    Earlier systems with the hydraulically operated switch seem to work well enough, although they can require more and more pressure before they light the lamps which you may not be aware of 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.

    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 as well as even the back EMF generated by the switch releasing the relay seems to be enough to cause it 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 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 such as Herb Adler has done. 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:

      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 can easily be about 1 ohm in cars of our age, i.e. about five times that of a pair of bulbs in parallel. So a total of say 1.25 ohms (parasitic resistances plus two 0.5 ohms in parallel) gives a maximum practical inrush current of 15 amps. This amount of current through the 1 ohm parasitic resistances and the 0.25 ohms of the bulb will 'lose' 4/5ths of the system voltage across the parasitic resistances, leaving only 1/5th for the bulb. However that 1/5th is enough to start the filament heating up, which reduces its resistance, which reduces the total current in the circuit, which reduces the voltage 'lost' 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 fixed parasitic resistances to the bulb filament. Eventually you end up with the majority of the system voltage across the bulb, and relatively little lost in the parasitic resistances. However it takes a finite time for this to happen, which is part of the reason why incandescent brake (for example) lights take longer to light than LED brake lights. Only part though, because some of the parasitic resistances are causing a drop in voltage for the LED light as well as for the incandescent bulbs. But LEDs will reach full brightness at a lower voltage than incandescent bulbs, and there is no element needing time to physically heat up and start to glow, and that is the main reason 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 it 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 hydraulic 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.


    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.

    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. Just specify polarity, length of wiring from relay mounting point to switch position, and switch terminal type if they are other than conventional spades. 10 each plus 3.95 (Second Class Signed-for 3 days or less) or 4.45 (First Class Signed-for) to the UK, other countries P&P on request. Payment by PayPal is preferred, to, or if you don't have a PayPal account yourself you can click this button and pay with your debit or credit card:
    Usually despatched within 24 hours of receipt of payment.

    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. 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.

    July 2013: Lately I've been aware that there is significant pedal pressure and retardation before the tell-tale comes on, and initially it is only coming on dimly unless the pedal is pressed quite firmly. As I still have the relay in-situ but not connected I compared the pedal pressure with and without, using a stick and various thicknesses of 'shim' between the pedal and the back of the steering wheel rim. I was quite concerned to find that without the relay about an inch more movement is required before they come on, so the relay is now connected! I was also going to invest in one of the pull-on switches I mention above, as I don't trust this switch long-term now, but after complaining the MGOC sent me a replacement FOC, which I have fitted and will be using with the relay. A test drive shows the tell-tale coming on at full brightness straight away, and at lighter pedal pressure than before, barely any retardation.

    Instrument Lights:

    Schematics:Up to 1969
      1970 and later

    These are powered from the 'parking' or first position of the main lighting switch. Originally all cars had a rheostat on between the speedo and the tach to progressively dim the lights. 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. 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 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 recessed, 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 up into the hole again.

    All the rheostats I have seen (various cars) have been of the printed circuit variety where various resistances are 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 - it is prone to burning out if operated for long periods at slightly below maximum brilliance (a relative term). They are quite expensive (at the time of writing 40 from Brown and Gammons in the UK, $83 from Moss in the US) for a) what they are and b) the use they are. 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.


    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 came 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, 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.

    However you will find the rheostat no longer works as it did. If you have all LED bulbs then 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 it will dim slightly. This because the LEDs draw so little current, which means very little (a couple of tungsten bulbs left) or virtually no (no tungsten bulbs left) voltage is dropped across the rheostat so all or nearly all the voltage is still there at the maximum dimming position. 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 LEDs you need to add 8.8w of load, which at 12v represents 16 ohms. This is a standard value at a typical 0.6w 5% tolerance metal film component, but you will need a 10W wire-wound power resistor, and these are available at 15 ohms. A more sophisticated alternative is to use the standard rheostat to control a power 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.

    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.

    Headlamp Flasher:

    Note: Until the dip-switch was moved to the column stalk the headlamp flasher was powered from the brown (unfused) 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.

    Reversing Lights:

    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. The only 'adjustment' is provided by two fibre 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 shim may be all that is required. OTOH a missing shim can cause it to be on when it shouldn't be. 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. Some have cut a hole in the side of the tunnel and fitted a cover plate to give access to the overdrive switch, this could be done on the other side for the reversing light switch as well.

    Map/Interior Lights and 'lights on' warning:

    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.

    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.

    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 carcass, 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 frame.

    'Lights on' warning: A simple 'lights on' warning buzzer 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) is shown in Inset 1, and an enhanced version that only operates from the drivers door is shown at Inset 2. The polarities of the diode 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.

     Door switches Added October 2011:

    BL door switches were always subject to water ingress and corrosion, 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 (at least) 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, 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 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 cars had a boot light (roadster) or load-space light (GT) from the 1971 model year onwards.

    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.

    North American side marker lights:

    Side marker lights appeared in the 1970 model year and were wired, unfused, to the blue circuit to come on with the headlights only (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:


    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.


    From the 1970 model year the front fog lights were wired to be available with the dipped beam if required.


    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.


    If adding lights yourself 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: "A rear fog lamp is permitted to operate independently of headlamp, position lamp or ignition systems." ( A 'tell-tale' indicator is required, which can be just a coloured tag visible when the switch is operated as well as a light.

    Rectangular fog (kerb-side) and spot lights as fitted to my V8.

    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 lights at least off, so they can better see you 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.

    Number Plate lights: Added 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!). These only have 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, overrider bolt, 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 unit back to the bullet connectors in the earth wires used for the reversing 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. Cars with the number plate lights mounted on the number plate backing plate (rubber bumper and North American split bumper) were provided with earth wires going back to the bullets for the reversing lights (also used for North American side markers).

      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 whenever the key was in, and an additional drivers door switch. This switch differed from the courtesy light switches in that it was insulated from the body and had two wires, a purple (always on, fused) supplying 12v and the other to the buzzer. Both switches have to be 'closed' to sound the buzzer, i.e. either the door being closed, or the key 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.


    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

    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.


    Where to mount them is a question that often crops up. Early cars had a grille mounted between the dash and the tunnel, with the radio above in the dash. With the American padded dash and from 1972 on UK cars the radio moved to a centre console where the grille used to be, so speakers have to be positioned elsewhere. A PO of my roadster had cut holes in the rear bulkhead under the hood, but as I didn't intend to have a radio I welded them back up. The V8 came with them in the trim panels immediately behind the door opening, but this did entail cutting into the metal panel. OK on a GT but not ideal in a roadster, however smaller speakers or ones that project further may fit without cutting. Surface mounted speakers could also be positioned on the parcel shelf in the roadster, but would need to be detachable to access the battery. From 1977 (US spec) and 78 (UK spec) door-mounted speakers were fitted by the factory, there have been questions from time to time about the routing of the cable into the doors from people who want to retrospectively use that location, the attached images show how this was done.

      Herb Adler puts twin speakers in the early centre console.

    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 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. 13H 9475 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.

    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.Reference
    56341733243JSRB1464 terminal/spade40 ohm20 ampsintermittentStarter relay
    BMK68533302BSRB1114 terminal, 5 spade76 ohm20 ampscontinuousD-type Overdrive, HRW
    UKC514633188H?3 terminal, 4 spade??continuousV8 cooling fan
    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 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 probably also 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.

    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.


    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. I've 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 specify Type A or Type B when ordering I've not found any information there as to which is which! The option is only available for the basic four-terminal 12v relay, not 6v, fused, dioded or five-terminal types. 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.

    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 the second wiring terminal 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, as follows:

    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 modern i.e. Bosch relays are 85 and 86 for the winding, and 30 and 87 for the contacts. On the basic single-pole, on-off relays used on the ignition and starter 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 an additional normally open contact 87, or a normally closed contact 87a.

    References: Comprehensive Lucas switchgear catalogue containing information on switches, relays, flashers, both classic and modern, 136 pages, 7MB. October 2016: Lucas Electrical seem to have removed their online catalogues (and the TVRNA site seems to have vanished altogether), but I have found another copy here. If useful I suggest you download a copy. Another Lucas relay and switchgear catalogue but including fuseboxes, some duplication with the above, but only 43 pages, 2.8MB. Basic Lucas relay, lamp and fusebox info., largest page is 90k for those with download limitations.


    See also these redrawn schematics from Dan Masters. Capable of being enlarged by several times and so easier to read, 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, something the Masters simplifications don't have.

    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 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, probably an audible warning for a limited period if the car was started without the drivers belt being fastened, plus a visual warning which may be continuous until the belt is fastened. May also illuminate the warning lamp as a test function during cranking with the belt fastened.

    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
    Mechanical Problems
    Electrical Problems - slow cranking
    Coil Boost Problems August 2014:
    "It Won't Start!"
    Modern Starters - 'Geared' vs 'Hi-Torque'
    Changing an inertia starter to a pre-engaged
    Jump Starting

      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 inertia starter and a remote solenoid on the inner wing was fitted to MkI cars. MkII and later had a pre-engaged starter with attached solenoid. 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. Rubber bumper cars had a 6v ignition system and the solenoid had an extra spade which was a 'boost' contact to connect full battery voltage to the 6v coil during cranking for better starting under adverse conditions. Note that chrome bumper 4-cylinder cars with 18V engines had the later 2M100 starter with the boost contact, but it was unused until rubber bumper production started. All V8s had the 2M100 starter with the coil boost system.

    Pre-engaged solenoid: August 2013

    The Workshop Manual makes no mention of it, but it looks like the pre-engaged solenoid has two windings - a pull-in as well as a hold-in. 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. 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, and 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 seem to explain Brian Shaw's problem. Regardless of whether 12v is connected to the battery stud or not, current will still flow through 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 current when the solenoid operates, so could overheat.

    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.

    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 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.

    Coil Boost Problems: 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.

    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 from the bottom 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 attached, 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.

    Modern Geared Starters:

    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. Originally it seems that these didn't have the extra 'boost' contact for rubber bumper ignition meaning you had to dispense with it (not ideal) or replicate the function with an additional relay, or possible a diode if you know what you are doing! Latterly some have been available with the additional contact. 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. 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.

    'Hi-Torque' Starters: Be careful with these! I've seen some and they sit somewhere between the original and the geared starters. It may be that they use more modern 'rare earth' permanent magnets instead of a wired stator and so do give more torque, but may not be as effective as the geared starters. However I have seen some geared starters 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. Geared starters seem to have the solenoid in line with the pinion and the motor to one side. In these the solenoid may be about the same size as the motor, or possibly even larger. In my opinion it is geared starters that bring the greatest benefits, and are worth paying more for. December 2016: Having said that at the time of writing Moss have a 'new, modern, high-efficiency, light-weight' alternative at half the price of the reconditioned/exchange originals - 65 as opposed to 130, so a very good deal price-wise, although I can't comment on the performance. This compares with 205 for a new geared type. Brown & Gammons have the original type at 93 plus 11 P&P, and Leacy at 80 including P&P and no exchange. MGOC have the original at 70 or geared at 179, both plus 7 P&P, so it pays to shop around.

     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.
  • Matt Dabney came up with the following suggestion in response to someone having starter problems (first continual cranking then no ignition) after fitting a hi-torque starter. Matt 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. Click the link for the schematic .
  • Jump-Starting: Updated December 2011

    Jump Leads
    Starter Pack

     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.

    I've just been made aware of this 'Startmonkey 400' from BMIHT. 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. However you would need to charge it regularly to make sure it was 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 plug. Personally I shall stick with my jump leads and mobile phone. Incidentally they also sell an emergency phone recharger for 45, but the first thing I get whenever I have a new phone is a lighter adapter charger, and these are usually just a few pounds. Your battery would have to be completely dead, and the your phone battery flat, to strand you then.

    August 2016: There are also 'super capacitor' jump packs around like this one from Jaycar Australia. 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. However like the battery packs they are expensive compared to jump leads, and you have to ask yourself how many times you've needed any of them.

    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.

    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 screwed in with (usually) two fibre spacer washers, 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. You will need to unbolt the rear crossmember from the chassis rails and lower the tail of the gearbox on a jack, as well as remove the centre arm-rest and pull back the tunnel carpet to reveal the removable panel, but even then it isn't easy to get at the switch.

    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, switches rarely if ever 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 lights will 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.


    Washers schematic

    Originally a manually operated pump, 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 them 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. In that case it saved a long 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 he 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.


    One speed or two?
    Parking Systems
    Intermittent Enhancement
    Which side do you park? Added October 2008


    MkI Roadster Single-speed
    MkI GT Single-speed
    1964-67 two-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.

    One speed or two?  Rewritten February 2012

    The Workshop Manuals show (electrically speaking) three different wiper systems - MkI roadsters; MkI GTs; a 2-speed version on Mk1 cars, and a different 2-speed version for MkII and later cars.

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

    The MkI GT had a round single-speed motor with a more complex parking circuit that involved the manual switch, and four wires. 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 1964-67 schematic in the Leyland Workshop Manual has an inset diagram of the wiper motor and switch showing two speeds but the earlier parking arrangement. I don't know what models this was fitted to.

    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 with a similar park circuit to the MkI GT, with five wires. The switch was changed again to give two 'on' positions and had an additional park contact, making four wires at the switch.


    Single-speed roadster systems had a basic normally-open 'on-off' toggle switch to connect an earth to the motor to cause it to run, and when that is switched off a park wiper contact and arc on the motor keeps an earth connected to the motor until it reaches the park position.

    Early single-speed GTs could have the same system, or a later system with a more consistent parking method.

    Two-speed systems used a more complex three-position manual switch that connects 12v to the slow and fast speed windings as required, but when switched off an additional contact on the switch - the park contact - is connected to the slow-speed contact. With the wipers not parked the motor park switch connects 12v to this park contact, which with the manual switch in the 'off' position is connected to the slow speed winding and causes the motor to continue to run. When the wipers reach the park position the motor park switch disconnects 12v from the park contact on the manual switch, and hence from the slow-speed winding, so the motor stops. 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.


    1977 and later models came with a flick-wipe feature by moving the stalk upwards (on RHD cars, LHD used the same switch mechanism but on the other side of the car so flick was down and the continuous speeds up). The manual switch was basically the same but with an additional non-latching contact to connect 12v to the slow-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, but it is relatively easy to tell the difference from the 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

    The square MkI roadster motors have a earth supplied from the switch and the 12v supply 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 the 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 noticeably short 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 - slow 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 controllable position. The parking circuit consists of two change-over systems - one at the manual switch and the other 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 wire that goes to the motor, to run the motor. When the manual switch is turned off the red/light-green is disconnected from earth and connected instead to the black/green 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. 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. While it is spinning down it becomes a dynamo generating a voltage at its windings. By shorting out the windings 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 - slow speed 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.

      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 instead of 12v, and the manual switch puts out 12v instead of earth to run the motor in either the slow or fast positions. The manual switch again has the changeover function which connects the slow-speed winding to the park switch 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. The wire colours and functions are as follows:

  • Green - 12v supply to motor parking switch and manual switch
  • Black - earth for motor and parking switch
  • Red/Light-green - slow speed connection to motor, 12v supplied from manual switch
  • Blue/Light-green - fast speed connection to motor, 12v supplied from manual switch
  • Brown/Light-green - parking switch circuit from motor to manual switch, linked by the manual switch in the 'off' position to the red/light-green slow speed wire. Carries 12v when wipers are not parked, earth when they are in the park position
  • 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 or D; A and B have a screw-on park switch 37H 2734 and D has the more common clip-on park switch 37H 6784. The brush plates also differ.

    February 2014:

    Click the thumbnail for how to test the round, GT single-speed and the later 2-speed wiper motors with the five-pin connector plug.

    Upgrading Mk1 roadster to two-speed
    As well as the motor you will need a suitable switch 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
    As above, although you only need to provide one additional wire for the second speed. 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 slow 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."


    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!

    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 slow 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 slow speed and 2.2 on the fast, so the fault was probably a partially burnt-out armature winding.

    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 and rides on a cam, 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.


    Added 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 slow 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.

    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.

    Smartscreen Intermittent Control 

    The MG Owners Club sells 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 I think 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.

    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 motors with the park switch on the domed cover over the main gear it's said that you can rotate the cover by 180 degrees. On the later motors with the plastic park switch and connector block combined it's said you can dig the plastic cam ring out of the main gear and rotate that 180 degrees. 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. But it may be possible to get tubes and wheelboxes out as an assembly, turn the wheelboxes over, reassemble, then refit.

    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 GTs always parked in front of the driver, as the gears and arms were always different between LHD and RHD, and LHD were common to all markets.

    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:

    1962not available Denmark
    1963 Originally Californian, exported to Norway Germany
    1964 USA Sweden
    1965 USA Sweden
    1966not available Holland
    1967 USAnot available
    1968 USAnot available
    1969 USA Sweden
    1972LHD V8
    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 70827H 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 bladesGWB 217
    HD5-296001Aug-72onLHD37H 2732Use GEU 70837H 4309BHA 5204Matt-black 12" arms and bladesGWB 217
    All  RHD37H 2732Use GEU 70837H 4308BHA 5205Matt-black 12" arms and bladesGWB 217

    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.

    Wire Colours, Terminal Numbering

    Wire Colours
    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 turn 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 turn signal 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.

    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 almost every contact 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.

    Wiring Harness Replacement

    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.

    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.

    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 vice-versa with the new.

    Tape the wires that come out of the new harness in the engine compartment to the thinnest part of the harness. If you leave them free you will end up having to pull a greater thickness through the firewall than you need.

    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 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 red/white 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 red/white 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 red/white 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 pinion is supposed to find it easier to slide up the spiral into engagement with the flywheel first. 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 (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.

    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 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 indeed prove to be the cause in Brian's case.

      "It fires occasionally but not enough to run"

    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.

      "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. It is boosted to 12v during cranking by the white/light-green circuit from the solenoid to the coil 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. This (on UK cars at least) is located high up on the firewall behind the dash on the right-hand side and is a black plastic tube labelled 'PEKTRON' with spade connectors each side. One side has a single white/red wire with a female spade connector coming from the starter relay, and the other has one or two green/orange wires on a male spade going to the handbrake switch, 'BRAKE' warning light, and brake pressure failure switch.

    As a quick fix remove disconnect one of the wires from the diode unit and tape up both items to stop them earthing. As a permanent fix you can replace the diode with any 100v, 1amp item. It should be connected so as to allow a +ve voltage to flow from the white/red wire to the green/orange(s) but not the other way. But it doesn't really do much except light the 'BRAKE' lamp while cranking as an indication the light is working. However if the handbrake is on the light will already be lit, so it really only comes into operation if one is not in the habit of using the handbrake. Testing the light seems reasonable on those cars with split brake lines as it is used to indicate brake imbalance. But on UK cars where it only acts as a 'handbrake on' warning light the testing of it seems completely superfluous to me.

    For the interested, the mode of failure is as follows: Turning on the ignition connects 12v to the green wire. If the handbrake is pulled up at the time its switch connects the 12v from the green onto the green/orange to light the 'BRAKE' warning light. The green/orange also goes to the brake warning diode, which if short-circuit allows the 12v to appear on the white/red that runs from the ignition switch to the starter relay. This will operate the relay and start cranking before the key is turned to the cranking position. So startled, you turn the ignition off again, only to find the starter is still cranking! This is because there is still 12v (or close to it) on the green even though the ignition is switched off at the key, as this era of cars also has the 6v coil and harness ballast, and the extra contact on the solenoid to give a full 12v 'boost' voltage to the coil. This 12v supply comes from the coil, backwards through the harness ballast, onto the white/brown at the fusebox, and through the fuse onto the green, incidentally keeping other ignition circuits powered as well. Now we have 12v on the green, the circuit is as before so keeping the starter relay operated. So once the relay has operated the solenoid the circuit is self-maintaining, until either the battery is disconnected or the handbrake is released. Dropping the handbrake is obviously the quickest and easiest - if you have the presence of mind to remember such an arcane 'feature' at the time!

      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, 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.