MGB & GT Forum

Need some help 1973 MGB electrical .

When I turn on the head lamps the LH turn signal is stuck on causing head lamps to dim
So is it in the switch?
I do not think it is in the column because the turn signals work fine, it only happens when you turn on the head lamps .
Is it in the tail lamp?
Looking forward to hear
Thanks
Jim J

Sounds like a grounding fault - "sneak current."

Have you had this car for a while, or is it new to you?

Start by cleaning the earthing points (black wires). Common places are the black bundles in a ring connector screwed to the right inner wing (pozi-drive screw), under the dash at the wiper motor, and the lamp holders themselves. The fixtures earth through the chassis - look at the sheetmetal nuts - they have teeth that cut through the paint to complete the circuit. Often, they become corroded, and the electricity finds an alternate path.

Then look at the the bullet connectors for corrosion. Clean, and apply some dielectric grease.

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Jim K is a grease-stained wretch

Also remove the bulbs one at a time from the left signal lights. They have been known to cross feed across the 2 terminals in the front light, but occasionally the rear can give problems....as suggested above make sure the light units are well grounded.

Still need help
Sent this out last year
Still have the problem ....Question could it be the turn signal flasher that has gone bad? and is it under the dash or in the engine compartment
Thanks

If your electrical system has not been modified there is nowhere in the schematic that the headlights and turn signal bulbs come together.

Turn signals green circuit. Headlights fundamentally red circuit.

Recently someone reported an incorrect bulb in the socket (non-two filament) allowed a weird bleedover.

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Hi Jim.

The turn signal flasher unit is mounted just behind the glove box, next to the wiper motor.

No, if the RH turn signals flash ok, then there is nothing wrong with the flasher unit.

The most likely thing is that the rear tail lamp assembly is not grounded correctly. The lamp grounds through the mounting studs and was originally fitted with special stamped tin nuts that had sharp edges that would cut through the paint when tightened to get a good ground. If the lamp body is not grounding, then the tail lamp circuit can find it's way to ground through the flasher filament.

The side lamp filament is fed by 12 volts, it shares a common ground with the flasher filament. If this path to ground through the lamp body is a bad connection, the voltage will go through the flasher filament, follow the turn signal wiring forward through the front flasher lamp and find a ground there.

Try hooking a wire from one of the lamp studs over to the main ground point at the left hand license plate mounting bolt. That should fix the problem.