Main lights (62-69):

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). Number plate lights mounted on the bumper overriders use a tortuous earth/ground route through the bulb socket, casing, plinth, overrider, bumper, and bumper iron before they get to the body ground! When restoring my car they did not work until I provided a wired ground shared with the reversing lights, standard on cars where the lights are mounted on the number plate backing plate.

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.

Main lights (70 on):

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, to a bolt near the fusebox. Number plate lights mounted on the bumper overriders use a tortuous earth/ground route through the bulb socket, casing, plinth, overrider, bumper, and bumper iron before they get to the body ground! When restoring my car they did not work until I provided a wired ground shared with the reversing lights, standard on cars where the lights are mounted on the number plate backing plate.

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.

Dip-switch:

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:

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 the positives stops in the dip and main positions 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.

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 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 loom-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 graphic for the schematic. 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 loom, 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. See this picture for the layout (the two fused relays on the right of the group of four are for other circuits).

Brake 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.

The only thing, short of trying to get hold of NOS items, seems to be to fit a relay, such that the brake light switch only switches the light load of the relay, it is the relay that switches the load of the lights. See this modified schematic.

The later mechanically operated as opposed to hydraulically operated switch can cause the brakes to stick on if the switch is screwed too far into the pedal box (brake master without servo) or pedal bracket (brake master with servo). There must be 1/8" of free play on the brake pedal as measured at the pedal pad. This free play is between the pedal and the push-rod i.e. at the pedal clevis pin and is quite difficult to ascertain.

Instrument Lights:

Click 'Main Lights' above for schematics.

Rheostat
Uprating

These are powered from the 'parking' or first position of the main lighting switch. Originally all cars had a rheostat on the dashboard 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 switch cover 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. From 77 onwards RHD cars had it on the lower edge of the dash under the speedo. LHD cars originally had it between the speedo and tach. Then North American 'padded dash without glovebox' cars had the simple on/off switch on the left of the column shroud. '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 on LHD cars had the rheostat on the extreme left-hand side.

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 resistance elements are obtained by having printed circuit tracks of various thickness and length switched in and out as required. Also on every car I have bought (various marques and models) with one, it has always been burned out, resulting in an even dimmer glow than usual at maximum 'brightness' (a relative term at the best of times). They are also quite expensive (£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. Unfortunately other years have two separate red/whites which occupy both spades on that connection, but you can still transfer one of them over to bypass the rheostat for those lamps to see the effect. If you want to bypass the rheostat permanently on these cars for all lamps then you will have to rig up some way of connecting the two red/white wires to the single spare spade, e.g. a Scotchlok connector (not always very reliable) or fabricate a 'Y' connector with one female spade and two male spades (a bit of a fiddle).

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. On the fuel gauge at least the light has to follow quite a tortuous path to get through to the front of the gauge as shown in these pictures. 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 (the fuel gauge here is an old spare).

A few years ago there was a recommendation from America to fit Radio Shack 7.5v bulbs, but given the running voltage on the car of 14.5v or so they were a bit like a firework - bright, but short-lived! Subsequently halogen lamps were recommended (again from America), giving significantly more light output. If they are significantly higher current items they could damage the rheostat when used en-masse, and if they are much higher heat output they could also affect the instruments, switches etc. The LBCarco items are 5w for the small gauges and 10w for the speedo and tach, i.e. twice to four times the wattage of standard items (they also recommend a 3w item for what they describe as 'green film' gauges, possibly because the higher heat output of the higher wattage items damages these gauges (see heat comparisons below). I've measured the current drawn by a standard 2.2W, a standard 4w, and a halogen 6w (all available in Halfords) and the halogen current is pro-rata with the tungstens at 200mA for the 2.2W, 300mA for the 4w, and 500mA for the 6w. However a set of 5w and 10w items will be drawing more 3 times more current through the rheostat than the standard bulbs. I've only been able to find 4w standard and 6w halogen bulbs with bayonet fittings in the UK not screw. Whilst the 4w is comparable in price to the standard 2.2w bulb the 6w halogen is about 5 times the price and the LBCarco items are 10 times the price of standard bulbs! However Tesco 12v halogen 5w and 10w capsule wire ended bulbs are about the same price as standard tungsten, and the wire ends could possibly be soldered into screw caps of old standard bulbs. The feature of halogen is that they are brighter than standard tungsten for a given current. Tungsten could be made this bright but they wouldn't last very long (like the Radio Shack items) as metal is evaporated off the filament more quickly, eventually causing burn-out. Halogen gas has the effect that when the bulb is switched off, the metal that has been evaporated off the filament migrates back to the filament again as it cools. Effectively this is like starting with a brand-new bulb each time you turn it on! The down side is that they do run much hotter for a given wattage: at 10C ambient the 2.2w runs at 30C, the 4w at 55C, and the halogen at a whopping 90C. As the bulb is at the bottom of the gauge (the fuel gauge at least) this may even contribute to higher than normal readings on both thermal gauges. Also halogen bulbs should not be handled with the fingers as oils will be deposited onto the surface which will form a burnt-on film reducing output, increasing heat and shortening life.

Another alternative that cropped up on the MG Enthusiast BBS was an electro-luminescent ring which fitted inside the gauge. A link to a photo was posted, but without a 2nd gauge with standard illumination for comparison, hence there was no indication of how much brighter it actually was. Taking photos of lights is always problematic and the gauge numbers were quite dim. Someone posted that they were interested, 'but can you make the picture a bit brighter'! I don't know whether the request was genuine or tongue in cheek, but it certainly made me laugh. Given that the 5w and 10w items are 2 and 4 times the output of the standard bulbs, maybe ordinary tungsten at that wattage (if available in the correct size and fitting) would be almost as effective run cooler, and be a lot cheaper.

Another option I'm following up is white LEDs. Very low current and heat, and the super-brights really are bright - forward facing anyway. This UltraLeds.co.uk site has loads of automotive LED bulbs, the instrument types at least being about twice the price of standard bulbs so not too bad, but postage is a bit steep at nearly 4 quid for a single bulb and VAT is also extra. Note that LED replacements for external incandescent bulbs may not be legal in the UK, even though manufacturers are installing LED arrays in many cars these days which are legal, and I've seen one site that states that even LED instrument lights are not legal on UK public roads. I looked around at Maplins and bought a single oval high-brightness, wide-angle LED as an experiment. Whilst very white and bright side-by-side with the standard incandescent yellow glow it is actually quite small, and inserted into the gauge it gave hardly any illumination at all. It is also a fiddle to use as one has to add a 1k resistor to limit current, and a diode to prevent reverse connection, as well as soldering it all to a screw-base to fit the car.

Given that the commercially available items contain four to six LEDs and are cheaper than I can buy all the bits for it just isn't worth the bother, so I ordered two LED bulbs from UltraLeds - one wide-angle and the other standard. Not too badly priced at £3 for the standard and £3.50 for the wide-angle, but post and packing added another £3.50 making each bulb about the same as Halfords 6w halogen. You could get a lot more bulbs for the same £3.50 p&p, though. These include six LEDs, a dropper resistor, and a diode array (for screw-in bulbs, a single diode for wedge types as these can be inserted either way round) so they will work with either polarity without damage. They are rated at 5w and so double the brightness of standard incandescents. The remainder of the pictures in this section show comparisons between them and standard incandescents in the tach and fuel gauges. In the fuel gauge they are whiter, but probably no more legible. In the tach they are significantly brighter making the instrument easier to read. With a mixture of incandescent and LED bulbs the rheostat only results in a very slight dimming of the LEDs (the incandescents dim as normal as they have a different voltage/brightness ratio) until it reaches the 'fully off' point, where they all switch off completely. With all LEDs installed there will be no dimming at all, just off or on, unless you replace the guts of the rheostat with a much higher value potentiometer or variable resistor, or use the standard rheostat to control an electronic circuit to dim them.

And 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?

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 top of the gearbox and the depth of engagement is controlled by two shims. A loose or worn switch can prevent the light coming on, or make it erratic, and 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.

Interior Lights and 'lights on' warning:

Interior/courtesy lights were optional from 1968 - 1970 (North America) or 1971 (UK), standard after that. The door switches have open contacts and can suffer from corrosion. AFAIK they are unobtainable and the closest replacements, whilst having a better construction, are visibly different and require the hole in the A-post to be opened out. 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-ground car, they should be reversed for a positive-ground car. Any 100v, 1 amp diode and 12v dc buzzer should suffice.

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 ground, shared with the headlights at the front and the reversing lights at the rear.

Fog & Spot lights:

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 a ground wire from the light unit back to the bullet connectors in the ground 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 ground wires going back to the bullets for the reversing lights.

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 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 opeing 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.

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 this schematic.

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:

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.

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:

References:

• Brake Balance and Handbrake Warning
• Dynamo and Alternator
• Electric Cooling Fans
• Gauges
• Hazard Warning
• Heated Rear Window
• Heater Fans
• Horns
• Ignition
• Ignition Switch Connections
• Lighting
• North American anti-runon valve
• Overdrive
• Seat Belt Warning
• Starter
• Turn Signals
• Washers
• Wipers

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.

The wires are crimped into a brass 'staple', for want of a better word, the wires and staple then being soldered. A heat-shrink end-cap is fitted over the junction first, then a length of conventional heat-shrink tubing over that, the two being shrunk over the soldered junction and that is all there is to it.

The chance of a fault developing inside one of these connections is highly unlikely bar severe abrasion of the insulation and hence shorting to metalwork, which is more likely to happen to a length of wire anyway.

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, successfully, 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, but what part that played in the logic I don't know, I've never seen a description. One wonders what different logic would need to be applied if the car was in a gear as opposed to not being in a gear. Whilst there is no need to disable the starting circuit there is no reason not to either. I don't know why a box of electronics was needed, the starter inhibition could have been achieved with a simple relay with a normally closed contact, operated at the same time as the warning light. Possibly the audible warning was on a timer, as with the later system, and possibly the visual warning was on a longer timer as on more modern cars. Although it shared the buzzer with the seat-belt system the 'key in, door open' operated independently. Presumably the drivers seat switch was required so that one could lean in and start the engine for maintenance reasons without having to have someone - or a large weight - in the seat with the belt fastened! Must still be a pain when manoeuvring the car in and out of the garage, though.

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. For 1975 and 76 only the same starter connection was used to trigger the service interval counter and warning lamp, which may not have been fitted to all cars.

UK 1977-on: Much like the later American system, but even simpler. No audible warning or 'key in, door open' function, a visual warning only was given if the car was started without the drivers belt being fastened, for a limited period. May also have illuminated the warning lamp as a test function during cranking.

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, but probably because of the higher current requirement of the pre-engaged starter a starter relay was eventually (1970 model) 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.

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.

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 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:

'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.

Geared/Hi-torque starters and positive earth/ground cars Added May 2008:
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 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. If fitting a modern geared or hi-torque pre-engaged starter to a Mk1 car you really ought to consider installing a starter relay or equivalent at the same time, to protect the ignition switch. I say 'equivalent' as 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 one cable and adding one wire, which is an excellent alternative to fitting a separate relay which needs more work to implement. Basically, on the existing remote solenoid, you remove the cable that goes down to the starter and connect it instead to the other terminal, i.e. the one that carries the battery cable. The other end of this cable goes to what would normally be the battery cable terminal on the solenoid of the new starter. The new wire is run from the existing solenoid terminal now vacated by the starter cable, down to the solenoid operate spade of the new starter. And that's it. Before and after diagrams can be seen by clicking on the thumbnail accompanying this paragraph. Needless to say, you must disconnect the battery earth/ground strap before starting any of these changes, and only reconnect when they are complete. Also just tap the ground connection back on briefly first just to check you haven't made a major wiring error - if you have you will generate a big spark, so protect your eyes and do it in a well ventilated space i.e. no battery gasses in the vicinity.

Jump-Starting: 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.

Either vehicle can be of either polarity (i.e. either positive or negative ground), 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, if you cannot see them check with a voltmeter. A voltmeter can also confirm which is the live terminal and which is the ground/body terminal. The MGB changed from positive ground to negative ground in 1967, other classic cars may be different, probably all modern cars are negative ground. 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 (for example Mercedes Parts and MGB parts) 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 grounded 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 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. There are also 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 ground.

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.

References:

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 ohmeter is not good enough. Ohmeters only pass a minute current through a circuit, switches rarely if ever have gold contact surfaces and so they will oxydise especially if not used for a while which presents a resistance to an ohmeter. 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.

Serial numbers (on the faceplate) were as follows:

In the current-operated tach coil current flows via the inductive pick-up on the back of or inside the tach, so the tach responds to the current pulses through the coil as the points open and close. If that circuit breaks the engine stops, if it shorts to ground you fry the loom! 1964-67 types had the pickup mounted on the outside of the case and the later one (68-72) had it mounted inside the case. For the earlier type a continuous loop of white wire comes out of the main harness from the coil SW terminal, through the pickup as indicated in the top picture on the left (click to expand), then back into the harness again towards the ignition switch. This is for positive ground cars. If the car is converted to negative ground the wire must be removed from the pickup and routed through in the other direction. If fitting a new harness I'm not sure if the ends of the loop are marked to indicate which is coil end and which is the switch end, if not you will just have to try first one way then the other. It won't hurt the tach if you get it the wrong way round. For the later type with internal pickup (negative ground cars) the ends of the loop of wire through the pickup are brought out to male and female bullet connectors mounted on the back of the case, see the lower picture on the left. The spade for the 12 supply to the tach electronics is close by the bullet connectors, and the spade for the ground connection for both the electronics and the instrument lighting is spot-welded to the back of the case. The harness now has separate white wires with female and male respectively bullet connectors, meaning incorrect connection is not possible.

With the voltage-operated type the ignition current goes direct from the switch to the coil, and a tapping off the coil -ve/points connection goes to the tach on a white/black wire, which responds to the voltage changes as the points open and close. If this circuit breaks the tach ceases to register and the engine continues to run. If it should happen to short to ground the engine will stop, but not fry the loom. (In fact this makes a nifty anti-theft device using a hidden normally open switch connected to the wire at the tach rather than in the engine compartment.) Since the current flowing through the coil has a direct relationship with the voltage at the coil CB or -ve terminal it follows that the two types indicate the same thing. Both types have a threshold above which any voltage or current pulse will register on the needle, and the relative sensitivities of the tach electronics and the engine are such that under normal circumstances weak ignition pulses will affect the engine before they affect the tach reading.

Typical problems are sticking, wavering, or simply not working at all. Sticking, where a rap with a knuckle on the glass fixes it, and it only occurs after being parked for a while or at certain times of year, is almost certainly a mechanical problem with the movement itself.

Wavering or flicking about, if accompanied by changes in the idle speed, have a good chance of being caused by bad connections in the ignition LT circuit that is ignition switch - coil (via tach where appropriate) - points - ground.

Wavering or flicking about not accompanied by changes in idle speed, randomly dropping to zero for longer periods, or not working at all, could be either the 12v supply to the tach, the connection between coil and tach on the later voltage-operated types, or electronic problems inside the tach itself. From 64 to 67 the tach was powered from a third white (unfused ignition) wire and black ground but after that it was from a green (fused ignition) and black ground for both current- and voltage operated types. In no case is the tach powered from the instrument voltage stabiliser as the output from this is 12v switched on and off about once a second and so is unsuitable for the tach for obvious reasons. Get a multi-meter with an rpm range, connect it to the points-side of the coil, and compare that with the cars tach. If they shows similar variations then there is a problem in the ignition LT circuit through the ignition switch, coil and points. If it is steady when the cars varies, and you have the voltage operated tach, then connect the multi-meter to the white/black at the tach. Variation here but not before would indicate problems with the white/black wire or connections between tach and coil. If that is steady too, or if it was steady at the coil and you have a current-operated tach, monitor the 12v supply and ground at the tach. If these are steady too then the problem must be inside the tach itself.

Updated May 2009: For information on the internal electronics of the tach see Mark Olsen's Sunbeam Tiger pages and Theo Smit's Tiger pages. However neither of these say much about the thermistor, this thread from The Sunbeam Owners Club of America states the original should have a value of 150 ohms at room temperature, but items in the 200 to 500 ohms should be able to be used successfully. A negative temperature coefficient (NTC) item is required, there are positive temperature coefficient (PTC) items around which are not suitable. Unfortunately suppliers in the UK only seem to stock items in the thousands of ohms, not hundreds of ohms.

If your inductive tach (64 to 72) doesn't work with your shiny new electronic ignition system try the Crane tip (page 16) of changing the wire going through the pickup from two passes (one turn) to one pass (half a turn) and recalibrating. You will need to dismantle the tach to get at the pick-up on later versions.

Fault diagnosis. By all accounts turn signals are the bane of an LBC-ers life. But like all things, it 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.

As well as straight-forward disconnections causing non-working turn signals, the MGB 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.

I suppose there was an element of 'bulb failure warning' in its design, modern flashers use electronics (instead of a heated bi-metallic strip) and flash rapidly if one of the main lamps fails, although there may be some aftermarket types that flash at the same rate regardless of load and therefore give no warning of lamp failure. Fitting of an electronic flasher unit only gets round the problem - probably bad connections somewhere along the line - temporarily. Eventually you will have to find and fix the root cause, you might as well do it now. But if you insist on copping out disconnect one of the bulbs with the new unit fitted and make sure that the flashing speed has changed. 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. In general OE electronic types (which should be OK) have three wires, the third wire being a connection to ground, whereas two-wire 'heavy duty' types are the ones to avoid. See below for LED Bulbs which also need to be treated with care. 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."

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. Again, you want to warn other road users for as long as possible. Hazard flashers can be useful in de-bugging turn signals.

The standard indicator flasher unit for an MGB is the Lucas 8FL unit, and for the hazards the Lucas 9FL

As mentioned before the turn signal 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 - ground - battery.

The hazard warning circuit is: Battery - heavy current cable - brown circuit - in-line fuse - another brown circuit - hazard flasher - hazard flasher switch - green/white (RH side) and green/red circuits (LH side) - turn lamp holder - turn lamp - turn lamp holder - black circuit - ground - 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 "They flash but so do other lamps" or "They don't cancel".

"They don't work at all"

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 turn signals 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 ground cars (later MGBs), connect the red wire from the buzzer to the green on the turn flasher and the black to the light-green/brown wire. If you use spade connectors on the wires from the buzzer you can connect and remove it simply by unplugging spades, no cutting or soldering of wires. For the earlier positive ground 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.

Click here for the 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 ground, the switch controls the ground 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 ground 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 with the horns in 1977, they had always been backed by 12v and a switched ground sounded them until then, then the horn button put out 12v and the horns were backed by a ground from their physical mounting. In that case it saved a long run of (purple) wire from the fusebox to the horns.

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.

Update May 2008: Niels Hansen has contacted me with information about an adapter harness that allows the single speed GT motor with the later parking system to work using the standard roadster harness, and also a correction to my schematics. Click the icon above for the schematics and here for a picture of the sub-harness.

Update March 2007: Keith Evans has contacted me with the following information on converting from the rare single-speed round motor to the 2-speed:

Update May 2006: Bruce Cunha has contacted me to say he has a round single speed motor on a 67 GT which on the face of it seemed to have the early park system with the contacts inside the main case riding on the gearwheel. However on further investigation it has not one but three contacts riding on the gearwheel and circuit-wise seems to equate to the later parking arrangement. See here for some of Bruce's pictures.

Updated Summer 2005: The Workshop Manuals show (electrically speaking) three different types of wiper motor - the single-speed with simple parking circuit; the early two-speed with simple parking circuit, both with a square motor housing; and the later two-speed with more sophisticated parking with a round motor housing. This and others sources imply that the single-speed and early two-speed were fitted to Mk1 roadsters, and the later two-speed to Mk2 and later roadsters and all GTs. However there seems to be a fourth variant 'in the field' on early GTs which has a single-speed motor in a round housing i.e. with the later parking arrangement.

If you are considering upgrading from single-speed to two-speed you should be aware of the differences in motor switch and wiring between the two types of two-speed system. Click here for schematics of all four types plus flick and intermittent (e.g. Smartscreen) wipe facilities.

The square motors have a ground supplied from the switch and the 12v supply at the motor, and three (single-speed) or four (two-speed) terminals and a simple parking circuit. This parking circuit consists of a contact running on an arc which has a break where the wipers are required to stop. The contact is connected to the 'normal' speed winding and the arc is connected to ground. Thus when the wipers are not parked the motor has an alternative ground supply to keep the motor 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. The wire colours and functions are as follows:

The round motor parking system differs in that it stops in a much more predictable and controllable position. The parking circuit consists of a changeover-switch that operates at the park position. This changeover contact is used to disconnect the power and literally short out the motor, and the effect of this is to stop it dead, so to speak. 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. The requirements of this type of parking circuit mean that the motor is backed by ground instead of 12v, and the manual switch puts out 12v instead of a ground to run the motor. The manual switch also has a 'normally closed' contact which connects the parking switch to the slow-speed winding. The parking switch supplies 12v (from the motor, via the manual switch and back to the motor) while the wipers are not parked, and a ground when they park. The parking switch has to be wired via the manual switch in this way because in normal use, every time the wipers passed their park position the parking switch would connect a ground to the winding, which would also have 12v connected to it, which would blow the green-circuit fuse. The wire colours and functions are as follows:

The above is for the later 2-speed round motor. 67 GTs seem to have had the round motor with the later parking system but they were only single-speed. The wire colours and functions are as follows (confirmed by Glenn G, Texas autumn 2005):

If you want to upgrade a single-speed square motor system to two-speeds, by using an 2-speed square motor you only have to run in one additional light-green wire from switch to motor. If you use the 2-speed round motor, which will be more readily available, you will have to run in two additional wires between motor and manual switch plus replace the ground at the manual switch with a connection to the green (fused ignition) circuit.

Upgrading from a round single-speed motor to a round 2-speed motor you will also need only one additional wire to the motor.

Whichever upgrade path you take you will also need to replace the 2-position switch with a 3-position. A square 2-speed motor will only require a simple switch which connects a ground to the slow speed winding or the fast speed winding, disconnecting from both to park. As well as a 2-speed GT wiper switch any toggle headlight switch will do the job. If using a round 2-speed motor as well as the switch needing contacts for slow and fast speeds it will also require a contact for the park circuit. Again a 2-speed GT wiper switch will suffice, but an early roadster headlight switch with several unused contacts can also be used.

Also available is a schematic for flick-wipe and intermittent wipe functionality.

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 less than 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 an 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. It also seems likely that all 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 both North America and elsewhere.

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 this makes interesting viewing:

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.

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

Roadster
Change-point				Motor	Comments	Gear	Arms	Comments	Blades
HN3-101	May-62	HN3-6916	RHD/LHD	17H 2013	Use GEU 714	57H 5589	BHA 4321	10.25" arms, 10" blades	GWB 202
HN3-6917	Feb-63	HN3-138400	RHD	57H 5599	Use GEU 714	47H 5307	37H 4952	Heavier (13 oz) wiper arms	GWB 202
HN3-6917	Feb-63	HN3-138400	LHD	57H 5599	Use GEU 714	47H 5307	BHA 4396	Heavier (13 oz) wiper arms	GWB 202
HN4-138401	Nov-67	HN4-158230	LHD NA	37H 2732	Use GEU 708	37H 3046	BHA 4816		GWB 202
HN4-138401	Nov-67	HN4-167576	RHD	37H 2732	Use GEU 708	37H 3045	BHA 4814		GWB 202
HN4-138401	Nov-67	HN4-167576	LHD not NA	37H 2732	Use GEU 708	37H 3046	BHA 4816		GWB 202
HN4-158231	Nov-68	HN4-164063	LHD NA	37H 2732	Use GEU 708	37H 3046	13H 5460	Triple wipers	GWB 202
HN4-164064	Dec-68	HN5-294250	LHD NA	37H 2732	Use GEU 708	37H 3046	BHA 4913	Magnatex arms instead of Lucas	GWB 141
HN4-167577	Feb-69	HN5-246076	RHD	37H 2732	Use GEU 708	37H 3045	BHA 4914	Magnatex arms instead of Lucas	GWB 141
HN4-167577	Feb-69	HN5-294250	LHD not NA	37H 2732	Use GEU 708	37H 3046	BHA 4915	Magnatex arms instead of Lucas	GWB 141
HN5-246077	Apr-71	HN5-294250	RHD	37H 2732	Use GEU 708	37H 3045	BHA 4913	LHD NA arms fitted	GWB 141
HN5-294251	Aug-72	HN5-410000	RHD	37H 2732	Use GEU 708	37H 3045	BHA 5201	Matt black arms and blades	GWB 216
HN5-294251	Aug-72	HN5-360300	LHD not NA	37H 2732	Use GEU 708	37H 3046	BHA 5203	Matt black arms and blades	GWB 216
HN5-294251	Aug-72	HN5-410000	LHD NA	37H 2732	Use GEU 708	37H 3046	BHA 5201	Matt black arms and blades (3)	GWB 216
HN5-360301	Sep-74	HN5-410000	LHD not NA	37H 2732	Use GEU 708	37H 3046	BHA 5201	NA arms fitted	GWB 216
HN5-410001	Jun-76	on	RHD	37H 8221		37H 3045	BHA 5201		GWB 184
HN5-410001	Jun-76	on	LHD	37H 8221		37H 3046	BHA 5201		GWB 184
GT
Change-point				Motor	Comments	Gear	Arms	Comments	Blades
HD3			RHD	27H 6409	Use GEU 708	27H 6420	BHA 4546	12" arms, 11" blades	GWB 142
HD3			LHD	27H 6429		27H 6424	BHA 4548	12" arms, 11" blades	GWB 142
HD4-138401	Nov-67	HD4-158230	RHD	37H 2732	Use GEU 708	37H 3047	BHA 4817	13" blades	GWB 143
HD4-138401	Nov-67	HD4-158230	LHD	37H 2732	Use GEU 708	37H 3048	BHA 4819	13" blades	GWB 143
HD4-158231	Nov-68	HD5-296000	RHD	37H 2732	Use GEU 708	37H 4308	BHA 4881	13" blades	GWB 144
HD4-158231	Nov-68	HD5-296000	LHD	37H 2732	Use GEU 708	37H 4309	BHA 4880	13" blades	GWB 144
HD5-296001	Aug-72	on	RHD	37H 2732	Use GEU 708	37H 4308	BHA 5205	Matt-black 12" arms and blades	GWB 217
HD5-296001	Aug-72	on	LHD	37H 2732	Use GEU 708	37H 4309	BHA 5204	Matt-black 12" arms and blades	GWB 217
V8
All			RHD	37H 2732	Use GEU 708	37H 4308	BHA 5205	Matt-black 12" arms and blades	GWB 217

Problems

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 ground 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.

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.

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 operates the washers as well. 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 if you manually switch them on and off instead of having them scraping back and fore when there isn't enough rain/spray.

There seem to be different versions for the Midget and what is described as 'rubber-bumpered MGB', but from the pictures and fitting instructions I suspect that the Midget unit is suitable for the MGB with single-speed and early two-speed wipers, and the other unit should be used for MGBs with the later two-speed wipers. This includes all but the earliest chrome-bumpered cars as well as rubber-bumpered cars, i.e. from 1968 on. The difference is how the park circuit works, see the schematic thumbnails on this page.

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.

Wire Colours. The most important colours to remember are:

• Brown - always hot, unfused, feeds everything except the starter either directly or via the purple, white and green circuits
• Purple - always hot, fused (bottom fuse in fuse-block), typically horns and interior lights
• White - ignition, unfused, typically coil, fuel pump, overdrive
• Green - ignition, fused (2nd fuse up), typically instruments, brake lights, reverse lights, turn signals, wipers, washers and heater fan
• Black - ground

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 schematics 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 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 turn signals 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.

Fusebox. Added October 2007
Unlike the 2-fuse fusebox the 4-fuse fusebox is 'handed' in that the front of the top two fuses are connected together as part of the splitting of the parking lights into two separate circuits with one fuse for each side. This link can only be seen from the rear, as shown by clicking the attached thumbnail, but if you have some funny electrics and think you may have fitted it the wrong way round (which will put the linked pair at the bottom rear) you can check from the front by looking for the terminal numbers. These are quite small and easy to miss (circled on the 2nd image). In fact the Lucas Part No. and week of manufacture are easier to spot ('rectangled' on the 2nd image) and these should also be at the top of the fusebox when fitted to the car the correct way round.

The 1st image also shows the riveted connections on the rear of the fusebox, which can suffer corrosion and bad connections. You may think that a solid connection here would be preferable, but the rivets allow the external spades to move from side to side while fitting the wiring connectors without twisting the fuse-holders, which would mis-align them with the end caps of the fuses, which would result in very small points of contact, so limiting current and resulting in volt-drops and hot-spots, which as well as affecting the performance of the electrics connected to that fuse this can also cause premature fuse failure. The third image shows typical corrosion that can develop on the copper fuse holders.

The terminal numbers count from 1 at the top front to 8 at the bottom rear, slightly illogical when you consider that the bottom two fuses are the originals carried over from the 2-fuse fuseboxes. If you are wondering what the three circular holes in the fusebox are for and have lost your cover, then the 4th image shows that the middle hole is for the cover locating peg and the two outer holes for spare fuses.

Fuses. Updated January 2007 As far as I am aware all the MGB fuses except one of the two for the sequential seat belt system are 17 amp continuous rated, 35 amp blow rated. The odd man out is 500mA.

Apart from the earliest cars some additional in-line 35 amp fuses protect various circuits. Watch out for the one for the hazards which has brown wires on both sides of the fuse. Also watch out for the electric fans on late cars - although these appear to be on the green circuit they have their own in-line 35 amp fuse which comes directly off the white/brown circuit (ignition relay), i.e. it is not associated with the usual green circuit which is fused from the second fuse up in the four-way fuse block. UK cars from 1977 have yet another subdivision of the green circuit with another in-line 35 amp fuses supplied by the white/brown (ignition relay) circuit feeding things like heated rear window, turn signals, heater fan and tach, which leaves the original green circuit fuse (2nd one up in the four-way fuse block) feeding things like reverse lights stop lights, washers, wipers, and circuits associated with the seat belt warning lamp and time delay buzzer.

You would be well advised to add fuses to the fuel pump and overdrive circuits, as both these have been known to short out and cause major harness damage. See Pump Fusing and Overdrive Fusing.

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.

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 loom 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 loom in the engine compartment to the thinnest part of the loom. 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 loom 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 ground wires but rely on the mechanical fixings. Consider adding ground 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 grounding 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 ground points and use Vaseline when bolting the ground 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 ground strap. Connect a meter set to display 12v between the battery ground 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 ground from somewhere. Don't reconnect the battery ground strap until you are sure there are no shorts.

This could mean several things like:

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"

"The solenoid is chattering"

"It spins the starter but not the engine"

"It cranks very slowly"

"It turns over but won't fire"

"It fires occasionally but not enough to run"

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

"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 with spade connectors each side. One side has a single white/red wire coming from the starter relay, and the other has one or two green/orange wires going to the handbrake switch, 'BRAKE' warning light, and brake pressure failure switch. In this picture you can see the white/red on the left and the green/orange on the right, and the diode unit has a male spade on one side and a female on the other so it cannot be connected round the wrong way. Don't be tempted to connect the two wires together (you are physically able to) as it will simply cause the fault condition. The body of the unit has the circuit symbol for a diode indicating the direction of normal current flow.

As a quick fix remove disconnect one of the wires from the diode unit and tape up both items to stop them grounding. 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 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 loom 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 loom 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!