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MG MGB GT V8 Factory Originals Technical - Headlight to starter problem

Ihave a standard Rover SD1 engine/gearbox/starter in a UK MGBGT which has developed a new trick which a more compitent sparky than me will instantly recognise.
If I use the flasher or turn on the headlights the starter engages.
I have checked the wiring fuses colum switches etc, but find no obvious fault but somewhere in that maze of wires the light circuit is feeding the starter solenoid it seems.
Any suggestions or help offered will be gratefully received.
D Thomas


maybe is that secret procedure how to start an MG :)
Did you done any changens (electrical) in near past? If yes, check that first if not start with ignition switch, then lights - there is voltage even when your car is off so that could be source of problem.
good luck

Trace back that starter wire on the solinoid. Although given the proximity the column looks the most likly candidate. Take off the cowl and look for bent spade connectors. Could be that your lights are earthing into the starter wire.

Hi D,

You don't say what year your car is but some of the late cars, 1977+ perhaps, have a nice little sneak circuit. There is a feed from the starter solenoid to, of all things, the brake and/or seatbelt warning lights. This is to provide a bulb-check when the engine is being cranked. The circuits are protected by a diode but sometimes the diode fails closed circuit and allows the starter to be fed through the failed diode from the bulb circuit, so starting the engine.

Something similar might be happening in your case. I'd agree with the first Peter and suggest taking off the wire from the solenoid and running another one to the solenoid and 'touch' it to a live source, so replicating the 'START' function of the ignition/ starter switch. If the engine starts, but there are no interference problems, run the new wire to the appropriate connector on the starter switch but disconnect the original wire first.

Finally, tape the ends of the disconnected wires and stow them out of harm's way.

Good luck

Peter (2)
P L Hills

Thanks for the advice and comments. It is a 1980 GT Peter.I have found lots of stray wires after opening up the looms carefully to find the person who did the conversion added new wires, Rover ignition, and a complex alarm system, and then taped over unused and new wires making a nightmare of spagetti not to mention corosion in the bullets etc. Anyway everything working now except for the Alternator warning light but that should be no problem. And to find that sneek circiut and kill it.
Next time around it will be a Dan Masters wiring setup to get rid of these stiff corroded wires!
D Thomas


Peter (2)'s mention of "sneak circuit" reminds me that I once read some web pages on this sort of problem caused by bad earths.

I think most of the problems mentioned were related to engines continueing to run (and not just dieseling) even after the ignition was turned off. The sneak circuit might have been (very hazy memory) something to do with faulty earthing of stop or tail lights.

I can't remember any more details other than it was on a MGB or Triumph website also.



This thread was discussed between 24/04/2006 and 01/05/2006

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