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MG TD TF 1500 - Negative Amps On A Lightly Used Generator

I have a 1952 MG TD/C that I keep running every weekend through summer, winter, spring, and fall. The problem that popped up this past weekend was a negative reading on the ammeter. The reading goes deeper into negative territory as I gently rev the engine.

The generator is only ten years-old; the previous generator was original to the car. The battery is five years-old, and I keep it on a trickle charge when I'm not driving the car.

Anybody got any suggestions on what's going on? Is the trickle charge burning up the battery? Is the generator dead or dying?

Erick in Virginia

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EB Blackwelder

Erick, it might not be the generator, unless a brush is hung up or a dirty commutator. It might be the control box. The points on the relays might be dirty and need cleaning, which I would check first. Just a guess. PJ
PJ Jennings

My simple method to test just the generator. Disconnect both leads at the generator, then connect a jumper lead from one terminal on the gen to the other. Then a voltmeter between the jumper lead and ground. Start the car and slowly increase idle speed, you should see a smoothly rising voltage but do not exceed 16 volts. If the voltage does increase the issue is probably with the regulator or wiring between the gen and regulator.
John Quilter (TD8986)

Did you by chance change how you installed the battery? Was your car Positive earth, and you mistakenly installed it Negative earth? The car will run either way. Worth a check, not the first time someone put a battery in negative ground in a positive ground car.
.. CR
CR Tyrell

This is my suspicion, I gave a detailed checklist on another forum to actually verify that there is an issue.

That was ignored, so I am out.

Things like tooting the horn, turning on the lights and watching the ammeter are free 10 second checks.

Watching the ammeter when the fuel pump click tells a great story.

A picture is worth 1,000 words.

Over and out.
P G Gilvarry

This thread was discussed between 07/05/2021 and 09/05/2021

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