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MG TD TF 1500 - I am back and have a problem


It has been a few years since I "finished" my 52TD restoration. As much as anyone ever finishes such a project. In any event I seek your advice. I tuned her up and had a problem with the choke cable that caused me to back off the dash slightly. When back together, the green generator light is now lighted and does not go out. This is wrong, right? The amp meter shows that above idle the battery is charging; however, the darn bulb won't extinguish. Before I start tearing things apart, I thought I would ask if anyone has an idea what might be wrong. Everything worked fine until I removed the dash.

Thanks in advance

Dave Rome

Are you sure it is the generator light and not low fuel light.

Generator lights are habitually red.

If the ammeter is going positive the generator is good.

P G Gilvarry

Interesting question. I shall check the wiring and see what is connected. That said, is it a reasonable test of the generator to monitor the output voltage? It doesn't appear to go above about 11 Volts (without removing any wires from the regulator).


Dave Rome

The output needs to be above 12 volts or the battery will not charge.

Tim Burchfield

Peter, your were correct. I re-wired the car 10 years ago and have not used it much for the past 4 or so. I guess I ran it low on gas while tuning it up and road testing. That light has never come on in the past, which I guess is a good thing as it proves it actually works. With respect to charging, my digital meter peaks at 11 volts, which I know is too low to charge; however, the other light is not illuminated. So I guess that bulb must be burned out. I shall check it out. I assume that the procedure in the shop manual is a good one to adjust the generator voltage?

Thanks all.

Dave Rome

Dave, you could connect the D and F terminal on the rear of the generator together and measure the voltage between there and earth, should be around 18 volts.
I would look at that before trying the regulator.
Don TF 4887 "Figaro' TC 1736 "Sibelius'
Don Walker

The generator light would come on when you turn the Ignition on, if you can get a very low idle it would be on too, should go out when you increase revs.

But you say ammeter goes positive? Turn headlights on with engine at a very low idle, you will see negative on the ammeter, when you increase revs it will go positive.

If that happens you should be ready to go.

P G Gilvarry

Surprising you can get your digital meter to read anything. Analog will always read in such an environment. 11 volts when?
J MacDonald

"Surprising you can get your digital meter to read anything. Analog will always read in such an environment."

J MacDonald is absolutely correct regarding digital multimeters. Digital multimeters have a sampling time in their operations and they are very accurate when they sample a voltage. The problem when taking a reading of a generator is that it puts out a pulsating voltage and if the digital sample of the voltage is taken when the pulse of voltage is very low, it is going to affect the average voltage that is displayed.

When working on a generator in a car, even a little $5.00 analog meter will by much more accurate than a $100 digital meter. Cheers - Dave
D.W. DuBois

I never thought about the sampling rate on a digital volt meter. I shall do the load thing (with the lights) and see if it comes on or I note negative current. You learn something every day.


Dave Rome

This thread was discussed between 29/04/2017 and 30/04/2017

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