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MG TD TF 1500 - Ignition waring light

My igniton warning light stays on after the car has been started. I installed a solid state voltage regular and had the generator rebuilt. My understanding is once the engine is runing the light should go off, what causes it to stay on all the time, and will it do any harm? I am ready to install the shield under the dash, but don't want to do that until I fix this problem
Any ideas or thoughts?
Louis Levin

Look for the obvious first. Belt tension and any loose/dirty connections including the battery.
Mike Hart

Be very careful with the belt tension. The T series generators do not need much tension on them and in fact, will be damaged by excessive tension. See the article, Keep Your Belts Loose in the Other Tech Articles section of my web site at:

Louis - See the article, Testing a Dynamo/Generator in the same section of my web site as above. Run this test on your generator to see if it is putting out the proper voltage. If you don't have an analog multimeter, pick up a cheap one at Radio Shack or at Home Depot or Lowe's, a digital meter is really not a good meter for doing this test. I assume that you got your solid state regulator from Bob Jeffers. If so, you might want to contact him for further tests. Bob is the real expert on the charging systems. Cheers - Dave
David DuBois

I'm betting the new generator wasn't polarized. Mine wasn't. Simple to do just in case.


Larry Karpman

Thanks guys. I did have the solid state done by Bob Jeffers, and yes the generator is polarized. I will get an analog multimeter and check to see if it putting out the proper voltage. I did take the car to the guy who rebuilt the generator and he said it was putting out the proper voltage. Oh Well, the car runs fine, so I guess I won't worry about the light being on all the time.
Louis Levin

David: My belt is loose, I read the article awhile ago and keep it loose. David you state in Testing A Dynamo " If the generator checks out reconnect the wires to the dynamo. Connect the multimeter between D terminal of the regulator (brown/yellow wire) and again start up and slowly increase the revs watching the voltmeter." My question is: connect the multimeter between D terminal and WHAT?
Thanks, Louis
Louis Levin

Louis, I've just been through this...and if your ignition light is staying on something is *wrong*. Yes, your car may be running fine for the moment but it's running off the battery which is not being recharged by the generator. Hopefully when the battery goes flat you're not too far from home because if you are you're going to end up being towed/trailered or pushed the rest of the way. If you start hearing an occasional miss head for've got about 30 miles left in the battery...and the miss will get worse as you get closer to the house to warn you that you don't have much time left.

If your generator is putting out the correct voltage then there is either something wrong with the wiring or with the regulator (and I have one of Bob's also...I love it).

Been there, done that, didn't enjoy it but bought the t-shirt anyway.

Gene Gillam

Louis - than you for bringing that omission to my attention. That should read between terminal D and ground.

"I did take the car to the guy who rebuilt the generator and he said it was putting out the proper voltage"

I had a shop tell me the same thing when the generator from our TD would not put out over 12 volts in the test with the two generator leads hooked together. When the shop ran the test that had to run the generator at a tremendous speed to even reach 12 volts, yet they still told me it was good. I just told them thank you very much and have never been back to them. I found a high resistance on the output of the generator, fixed the problem and retested it on the. When working properly, the generator will run right up to 20 volts at less than 1500 rpm and will continue to go up very rapidly until it burns itself up if the rpm is increased further (that is why the test procedure states that the voltage should never be allowed to go beyond 20 volts). Bottom line, I have always been suspicious of auto electric shops until I see how they run their tests and interpret the results. Cheers - Dave
David DuBois

Louis, Try this. With your engine running, and the red ignition light glowing, disconnect a battery terminal. If the engine stalls, then you know for sure that you have a charging problem, and should not be driving the car until it is corrected. Hope this helps. Phil
Phil Atrill

What's the ammeter have to say?

If your warning light is correct, then the ammeter needle is never on the charging side.

Jim Northrup

The ammeter is in the middle, when I turn on the lights it goes to the neg.side
Louis Levin

What about at normal engine in driving it centered, or a bit to the plus/neg...?

Gordon: When I am driving along, like I did yesterday afternoon, with the top down and the sun in my face, the needle is in the middle and ever so slightly moving to neg., other words a bit to the neg. side
Louis Levin


If you're driving your car the ammeter should be reading slightly positive unless your battery is fully charged. If it's reading negative your generator/regulator is not charging the battery.


Gene Gillam

This thread was discussed between 04/03/2010 and 07/03/2010

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