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MG MGA - Spark, smoke, burned finger and now no headlights

Oh how I hate bullet connectors. Driving down to Rhode Island everything was going great untill 1 mile from our destination when spark, smoke from under the instament panel. An exposed wire on a bullet connector touched the rapping of the oil gauge preasure line. Of course I touched it. Now I have a nice burn on my finger and no headlight. The headlights worked the day before (state inspection day). They were not on when the sparking happened. Everything else works, tail lights, running lights, wipers interior lights, just not the headlights. Since I am in Rhode Islane I don't have a wiring diagram, or many tools. Suggestions? Are the lights avaliable at most auto parts stores or only through Moss etc? Thanks
R Egge

In my opinion it sounds like the bullet has been fitted to the wrong side of the joined cable. I usually fit the male bullet to the earth wire so that if it touches any casings or pipes there is no potential difference. Obviously, the female bullet goes on the live side and is shielded if it comes into contact with any casings or pipework. My car is negative earth. Same principle applies for positive earth. Just think it through.

Sorry Russell, that does not answer your question directly, just food for thought when making up connections.

Steve Gyles

What colour was the wire that touched the oil gauge capiliary?
Bob Turbo Midget England

I think it was a black wire. Got to go and try to drive home in the rain. The joys of old british sports cars
R Egge

In theory, wires with black insulation are usually earth wires.

If it only is the headlights that have been affected then you probably need to check out the main lighting circuit.

On a 1600 under the dashboard the wire colours should be as follows:-

BROWN/BLUE wire is main live feed from control box (regulator)(A1 terminal). This feeds power to the ignition switch.

When switched on the ignition feeds the main and dipped headlights through the BLUE/WHITE wire which leads through to the main lights switch and on through to the main/dip switch.

The RED wire from the main light switch feeds the front and rear sidelights,panel lights through the rheostat, map light and also the fog light if fitted.

So I would check out the BLUE/WHITE wire first to see where it has shorted through to earth.

Unfortunately I know from experience that if you have had a short circuit for more than a few seconds on the lighting circuit then you most probably have some wiring to replace under there.

When you fix it I would strongly recommend that you fit an in-line fuse to the lighting circuit as it may save you hundeds of dollars if you have to replace the loom.
Best of luck

Colyn Firth

All bullets are male. Two bullets will be joined with a female snap connector (like a tube).

There are very few (original) bullet connectors behind the dash. One is a NB wire form the horn. Ground that one and horn will sound. Another is a green wire from the switched fuse (supply for the blower switch). Grounding that one should blow the fuse. None of this has anything to do with headlights. See here:

Someone may be confusing snap (bullet) connectors with Lucar (spade) connectors. Lucar connectors are male and female. The male part is nearly always part of an electrical device with the female part being on the connecting wire. There are (originally) very few of these anywhere on the MGA. When they are used on MGA the female part is usually NOT insulated.

I believe the MGA 1500 originally had no Lucar connectors anywhere in the car. Late production 1600 and 1600-MK-II used Lucar connectors on the generator and control box.

One of the more recent sins is that an aftermarket ignition switch will commonly have Lucar connectors. I have multiple articles involving that problem on my web site. Power supply running from the control box to the ignition switch is a fat NU wire. Another NU wire runs from ignition switch to the lighting switch. See here:

These NU wires are always hot from the battery and not fused. With the aftermarket ignition switch it is common for one of the Lucar female connectors to lose its grip and fall off of the male terminal post. It is more often the supply wire carrying up to 20 amps in normal service. If that one is disconnected everything in the car goes dead. If the other one is disconnected all of the lighting goes dead not just the headlights (but brake lights and turn signals may still work).

My best guess is, the NU wire from ignition switch to light switch came loose from the light switch end, fell onto something else (temperature sensor line maybe) and shorted out.
Barney Gaylord


Am I correct in assuming that neither dip or main beam works.

If that is the case the fault has to be on the lighting switch side of the dip switch unless, as is unlikely, both dip and main wiring are damaged. If the side (running) lights are still working then power is getting to the lighting switch OK. It looks like a fault on the blue wire from lighting switch to dip switch but as the lights were not on at the time it is hard to work out how it got damaged unless something hot contacted it. If this is the case you should be able to spot the damaged insulation.

I've just had a look behind my dashboard and there are no bullet connectors anywhere near the oil gauge. It sounds like you have some unofficial wiring especially if it was a black wire that caused the problem.

Malcolm Asquith

Ok my bad.

Don't you hate it when two things happen at the same time. In addition to the sparkes, smoke and burned finger I lost the ground for the headlight. Cleaned off the area around where the ground was attached and ... now I have headlight. Sorry for the confusion. Totally unrelated except for timing

R Egge


I have both bullet and female connectors that crimp directly onto cables. Unless I am joining more than 2 wires together I do not need a separate female snap connector as you describe.

Steve Gyles

If you don't mind non-original connectors, I like gas-tight crimp-on butt connectors. Good for joining up to two wires on each end, eliminates bullet connectors, almost the same as welding the wires together, faster than soldering, insulation included. I haven't had one fail in 20 years of constant use.

The first place I use these is the bundle of connections just aft of the RR wheel joining side harness to rear harness. Crimp all of these connections, wrap the whole bundle with tape, and tape it to the bumper bracket for strain relief. After more than 20 years of use I had to remove the tape once to R&R the harness during recent body restoration work. When the electrical connections out last the car body I figure it's pretty reliable.

Snap connectors at this point (between side and rear harness) were used as a matter of assembly convenience during original production. It is not necessary to ever disassemble these connections, as the side and rear harness can be removed from the car without unplugging it here.

I usually retain the snap connectors (not always) for end devices, like headlamps and parking lamps with pigtails. To make these connectors reliable, clean the bullets, install a new female snap sleeve and stuff it full of silicone grease during assembly. Wrapping the bundle of connectors with tape keeps out road splash and helps immensely with strain relief. In the front corners BELOW the air pan (for easy access) I have no trouble with this system, even though it is exposed to road splash.
Barney Gaylord

I understand where you are coming from now Barney. I got the impression that you did not think crimped female bullets were available. All my harness is as standard, including connectors. It is just where I have fitted extra bits, such as the reversing light, that I have fitted the bullets in a 'safe manner'.

Steve Gyles

I have some female bullets on hand (not on my MG), just don't like snap connectors in general.
Barney Gaylord


What did you mean by 'gas-tight' connectors? Not a term I have heard before.

Steve Gyles

It means to crimp the connector tight enough that it excludes air from the joint (gas-tight). This is very corrosion resistant, similar to a solder joint. Much the same effect as packing the joint with silicone grease. Bottom line is, you have to use the right terminals and the right crimping tool. See here:
Barney Gaylord

This thread was discussed between 23/07/2010 and 27/07/2010

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