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MG MGB Technical - Starter motor problems

Re 71 roadster.
When turning the key to start the motor, the starter motor is operating before it should do. It is turning when the key is in the position before the starting position. The starter continues to run even when the engine is running.
When I reach to the wires at the back of the ignition switch, moving the red and white wire the starter intermittently will start and stop.
It seems to me there is a problem with the switch but would welcome any other views on this.
Thanks Trev
Trevor Harvey

Its in that area, either the switch is shorting from the ignition to the solenoid contacts, or perhaps the wires are shorting after the switch. It cant be before as the motor would run ign off.
Stan Best

Thanks for your reply Stan.
I have removed the switch from the key barrel,it all looks OK externally, no wires are touching and it seems to turn OK. Wondered if there is a way of testing the switch? With the switch in the position before it should start, wiggling the red and white wire terminal, it will intermittently start and stop. I notice from the wiring diagram this wire goes to the starter relay. wondered if the problem could be with this, but I think it is probably the switch.
Trevor Harvey

If you wiggle the 2 wires that were causing the starter to run now, does it still happen? If not then it points to the switch. Are the terminals solidly located or can you move them around to where they will touch inside or outside. The starter relay will only do what its told, 12v on the coil and it will spin the starter up. Since its a long way from the key switch, not likely its where the short is. If I was going to check this out further rather than change the switch I would find a spare switch and rig it up inside the car so the ign on went to it and the wire to the relay on the other pole. If you leave it on and the starter runs uncommanded then opening it will stop it. proof its the switch not the wires or the relay. Although fun this would be a lot of work.
Stan Best

Almost certainly the switch, the chances of it being the white/red starter relay wire shorting to the white ignition wire in the harness is minimal. Take the white/red off the switch, connect a voltmeter or test-lamp to the switch terminal and waggle it with the ignition on. If you see voltage then it is the switch. If not with the white/red off the switch and the ignition on waggle the wires, and if the starter operates then it *is* the wiring.
PaulH Solihull

I tested the switch as suggested by Paul, and no fault was showing. so I removed the switch completely from the wiring with the intention of taking it to pieces to have a better look at it. I then noticed that a single strand of fine copper wire laid across a couple of the terminals. This must have been there for a long while and why it has just started causing a problem, I don't know but it looks like this has been the cause of the problem.
Thanks for your advice Paul and Stan.
Trev
Trevor Harvey

This thread was discussed between 06/11/2010 and 09/11/2010

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