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MG MGA - Electrical question

My MkII has a few times just quit running. I suspect electrical and while checking voltage I see 13.4 volts at the starter solenoid, however with the ignition on (engine not running) I see
11.34 volts at the battery side of the coil. Should the voltage be the same?
Ray Ammeter


If you are losing 2 volts with the coil on and drawing 4 amps or so then it looks like you have a surplus resistance of 500 milliohms in your ignition circuit. If your battery is healthy (i.e. starts the car alright) and it's internal resistance is negligible then it could be that the 500 mohms is coming from a bad contact somewhere or maybe from the ignition switch itself.

You could try rewiring the switch but I think I would investigate with your voltmeter. Keep your earth meter lead fixed and check the voltage back from the battery side of the coil to the fuse box (A3) first then both sides of the switch then the control box (A1) terminal finally to the battery itself (use a long piece of wire). The point where it jumps the 2 volts will tell you where the extra resistance is.

I think I would make a preliminary check to confirm that the battery is only delivering 3 or 4 amps to the coil and the occasional similar value pulse to the pump........................Mike
Mike Moore

Thanks Mike. I am away from the car at this time. When I get back I will start checking the circuit as you suggested.

Ray Ammeter

A pre check may be to see if anything on he route is warm!
Paul Dean

Mike and Paul,
I did some voltage checks at the fuses and the voltage regulator.
I found the voltage was less by about 2 volts than at the starter solenoid. During this process I found the voltage was dropping. The battery is about 14 years old. I leave a Battery Tender hooked up to it all the time. So a new battery is needed. I did check the temperature at the fuses and at the voltage regulator while leaving the ignition on. The temperature difference was about 3 degrees F higher at the voltage regulator. I need to further investigate that. The external connections look good and clean, but internally may be a problem.
Ray Ammeter

This thread was discussed between 18/09/2016 and 26/09/2016

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