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MG TD TF 1500 - dynamo light on all the time still charging...

So... grandpa had this car before me and he always had an issue where the charging light would come on intermittently. I finally decided to have the regulator and dynamo looked at. When reviewed. It was found that it wasalways charging, but not very much. When they looked into it further, they found that the armeteur was burned out.

They rebuilt the dynamo and tested it with the regulator and all checked out okay. I put it back in the car and it did work, but the red charging light was on all the time. Based on the ammeter, it was still charging just fine. I put a meter on the battery and it was reading about 14 volts (as expected).

In a veryshort number of miles of opperation like this, the light went out and does not come on at all. I checked the battery voltage again and it now reads 12-13 volts. I checked the light bulb and it still has continuity.

Isuspect that perhaps ive burned the armeteur out again. Can anyone recomend any tests i can do on the cars wiring to make sure the wiring is not the issue?

Note: i checked that the connections at the dynamo ad voltage regulator are correct, and the car still does charge.

Alex
Alex Waugh

Alex, Have you followed the steps in the Workshop Manual for checking the operation of the generator and regulator? Matt
Matt Davis

Alex - Check that one side or the other of your ignition light socket is NOT going to ground. Cheers - Dave
David DuBois

Dave,

Is there supposed to be an insulator in there between the light and the dash? If it wasn't there could that cause the gen to short out and burn the armeteur?

Alex
Alex Waugh

Go To www.wiltoae.com there is a page labled "precautions-----" on it you will find three tests of the generator without the regulator. If the generator passes those tests it is good. The problem would then be in your regulator. If the generator fails any of those tests you still have a generator problem.

Good luck!
Bob
Bob Jeffers

Alex,

The ignition (and fuel warning) socket is bakelight (a plastic). There are two wires going to the base, in the case of the ignition light, one side is the white wire from the ignition switch, the other an output from the generator via terminal D on the regulator.

When the generator voltage balances with the battery voltage, there is no light. If the generator voltage is less, the battery has the higher potential and the generator acts as a ground for the light. Note that this lamp is a wound wire resistance lamp. If the wire is missing, a 48 ohm resistor will work fine to drop the voltage from 14 volts to approximatly 2 volts with the 250 milliamps of current needed for the proper bulb. (14-2)/.25 is 48.

warmly,
dave
Dave Braun

Will check this out and see what I find and report back. After this weekend, the generator and regulator go back to Romain Electric here in town that did the work for testing and review.

Alex
Alex Waugh

Okay... solved it! Took the gen and regulator back to the shop that rebuilt them and they tested out okay. I then started snooping the wiring. I found that the dash sockets were wired with the center red jewel as "fuel warning" and drivers side blue jewel wired as generator. However, the light bulbs were inserted as generator in the middle and fuel on drivers.

The basic take away here is that the wiring was not correct in a couple of different ways. So, I swapped the wiring to the sockets so that the center red jewel had the "12v at key on" wiried to it, and the driveres side bule jewel had the "green with black" wire in place. I then put the generator light bulb (yellow wire) in the center socket, and the green with black wired socket in the drivers socket and now my generator light works as it is supposed to!! In ALL the years that grandpa owned the car (since 1974), the generator light never worked correctly.

Sometimes it's the small things that matter!

Alex
Alex Waugh

This thread was discussed between 14/10/2011 and 23/10/2011

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