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MG MGB GT V8 Factory Originals Technical - Factory V8 Starter Wiring

Help!!!

I've just replaced the starter motor on my 74 factory V8 and now it turns over and starts (you can hear the engine firing) but when I back the key off to position two it dies. I've spent about half an hour staring at the circuit diagram to try and work out probable cause, but the diagram itself doesn't make sense.

The bit that I don't think makes sense is that the positive side of the coil is permanently connected (via a 4 way connector) to BOTH the spade terminals on the solenoid and the starter relay output. This would mean that with the engine is running the solenoid input would be live from the +ve side of the coil. This can't be right can it?

Is the four way connector a misprint? Should it be a pair of 2 way connectors one of which connects the starter relay to the solenoid input and the other connects the solenoid output to the +ve side of the coil.

Thinking about it, I think I may have a fault in the ballasted feed to the coil does anybody know what the resistance of the ballast resistor should be? I cant find it in the manual anywhere

Thanks in advance

Phil
Philip Shingler

I'd say you're right on both counts. It should be 2 2way connectors & you have an o/c to the coil +ve. I don't have a factory V8, but on my car the ballast resistor is incorporated in the wire from the coil to the 2nd fuse (white leads). You should check this lead for continuity. Barrie E
Barrie Egerton

I am not very familiar with the wiring of V8 starters, but if you have a coil with ballast resistor, then you should have a feed from the solenoid to the coil: this gives your boosted voltage when you are starting the engine. It does sound as though you have an open circuit ballast resistor and thus the engine dies when you disconnect the feed from the starter solenoid.
T Green

FWIW the problem was a fault with the new starter motor, both the spade terminals on the solenoid are connected to the the solenoid coil input (zero impedance between the two terminals) I managed to start the car without the coil boost feed connected, but the starter's going back to the supplier tomorrow. Luckily I can just slide the motor out past the header so this isn't as bad as it sounds. I'm going to take my multimeter with me and check the next one on the sales counter!

Thanks anyway

Phil

Philip Shingler

Phil, where did you get your replacement starter motor from? I am interested both in the fact that it is small enough to pass the headers and in avoiding the problem which you have had.
ian thomson

I got it from Moss, std factory Lucas unit reconditioned. My headers however are not std. I bought them from Mike the Pipe about 2 years ago, not helpful because I think he's now retired. The tricky bit was getting the top mntg bolt out. I used one of those Halfords ratchet spanners - best buy I've made in ages, without it I'd still be out there putting the exhaust back on. FWIW I tried to demo the fault to the guy on the desk and it wouldnt replicate. So I guess there must be a bit of swarf or something in the solenoid which caused a temporary short. So it could have passed Quality Control at the reconditioners because the fault didnt occur when they checked it. Still Moss were happy to exchange it so no worries now. If you've got a space problem I've still got the Quinton Hazel starter unit which I took off. It's actually slightly smaller than the Lucas one. It would need rewinding (it lost the bush at the pinion end so the rotor was able to touch the field coils = v short lifespan) but the solenoid's OK
Philip Shingler

Even though the usual cause of that symptom is a break in the main feed to the coil via the loom ballast, so that the only time power is supplied to the coil is from the ballast bypass contact on the solenoid, in this case because the bypass and solenoid operate contacts were connected together the loom ballast was trying to feed the solenoid as well as the coil. Because the solenoid is very low impedance in relation to the coil it resulted in much more voltage being dropped across the ballast then normal, leaving virtually none for the coil.

I've got the opposite problem - just replaced the starter and have no ballast bypass. But I was able to replace it without touching either the (tubular) manifold or rack.
Paul Hunt

This thread was discussed between 25/06/2002 and 30/06/2002

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