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MG TD TF 1500 - Ignition light on my TF, now DOA

Over a period of several months, the red ignition light on my TF has become progressively dimmer and dimmer. Now it doesn't show at all.

Any suggestions?

Gord Clark
Rockburn, Qué.
Gord Clark

Gord, under what conditions? How's your battery? Bud
Bud Krueger

Under all conditions, regardless of revs. It just never cones on any more. Battery is new. Generator is new two years ago.

Under no load, no lights, no heater, used to be off as long as I was charging, which I believe, is normal. But as revs dropped, lamp used to came on. But now, at idle, it doesn't show at all.

Does not come on, when I turn on the ignition. Gas light (blue) and turn indicator (green) work OK.

Is there a coil or some sort of resistance in this circuit?

Would the bulb degrade? Never thought of that.

This degradation has taken place over about a year.


Gord Clark
Rockburn, Qué
Gord Clark

Could be a duff bulb or a loose fitting bulb or corrosion or bad connection.
Dave H
Dave Hill

The lamp socket has a built in resistor, but I would suspect a poor ground.
The lamp socket makes ground through the instrument cluster plate. I t is held there by a spring and nut.
Try pushing in and wiggleing the lamp holder to improve contact.
Also check the ground on the panel. It’s usually a lug on a stud.

Jim B
JA Benjamin

Had to get back to my computer for picture.
Its a helical spring and c-spring.
The resistors, (on mine) are resistance wire wound around the OD of the housing. That wire cannot be soldered. contacts are compression. If they corrode fixing them is difficult.

Mine were broken. You can check continuity to see if OK. remove bulb and check from terminal to center bulb contact inside of housing.
You can also check continuity from terminal to ground wit a known good bulb inserted.

Jim B.

JA Benjamin

Gord, see http://www.ttalk.info/Tech/Indicators.htm for how the Ignition Lamp is hooked up. The lamp is not connected to ground. It's connected, through 75 ohms worth of wiring, between the ungrounded side of the battery and the output of the generator. When you first tun on the key the lamp is being lit up by the battery voltage to ground through the generator wirings.
How's your Petrol Warning Light look? Try swapping the bulbs between the two sockets and see what happens. Bud
Bud Krueger

Bud is correct.

MY BAD

No ground both side of the bulb have terminals
Check them to see if they are tight.

Jim B.
JA Benjamin

Will have a look at it tomorrow. Fact is, that the dash has never been disturbed in 64 years.

All your suggestions are plausible and most certainly worth a try. I should have done this 15 years ago when I could still bend. It will indeed, be a challenge to work under the dash.

Thanks for all your suggestions. I will report the results.

Gord Clark
Rockburn, Qué.
Gord Clark

I have had bulbs dim then fail, I just had one on a Subaru. I would suspect the bulb first, resister wire on the socket second. The clue is the fading before going out. A wiring problem would more likely faded much more quickly, if not instantly.
D. Sander

This thread was discussed between 22/09/2018 and 27/09/2018

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