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MG TD TF 1500 - Faulty Ignition Switch??

After testing the dynamo and voltage regulator and deciding to replace the VR, I hooked all the wires back up and sat down for a cold one. After about 10 - 15 minutes some intuition told me to take a look and I found that, with the key firmly in the OFF position the ingition light was brightly on and the VR was quite hot. I disconnected the F and D wires from the dynamo and was surprised to get quite a spark when disconnecting the D wire. Disconnecting those wires made the ignition light go out and the VR seemed to not be getting any hotter. Out of an abundance of caution I went ahead and disconnected the battery. Now I'm afraid that maybe the ignition swith is faulty (making contact when it should be OFF.

Does that sound right? Would that cause the big spark when disconnecting the D wire from the dynamo?

I'm thinking of installing a panel switch to ensure that the system really shuts off when the key is off. My thought is a double pole 30 amp toggle switch to positively disconnect both the D and F wires from the dynamo. Does that sound reasonable? As the song says - paranoia runs deep.


'53 TD
J K Chapin

jud, i am not a sparks guy...but in response to your idea about the panel you maybe aware, but if not, there are cars with a battery disconnect installed...these can be installed either on a battery post or the style that can be installed in a discreet location if desired..that installation will then also double as an anti- theft device...
the car has survived 60+ years without needing a panel switch..i believe once you get the sparks sorted out i believe you will lose interest in the panel switch..which, as you know won't solve your root problem.
perhaps the reverse cut out relay in the VR?..but i'm not a sparks guy..they will check in shortly.
good luck, regards, tom
tom peterson

I think that Tom nailed it - the cutout relay in the voltage regulator is stuck closed. This is about the only thing short of a total wiring screw up that would cause the situation. Cheers - Dave
David DuBois

I think a main cut-off switch is quite important. My mate's TD went up in smoke twice last year. Here's a photo of what I fitted (horn removed for installation).

Declan Burns

It's cable operated via the lever under the dash.

Declan Burns

Thanks. I also thought that it might be the cutout relay but it is very comforting to get your confirmation. So now the plan is a fixed voltage regulator to make it do right and a battery disconnect switch for peace of mind.

J K Chapin

Well, it's not beautiful or as elegant as Declan's but it's what I had hanging on the wall and it's pretty easy to tell off from on.


J K Chapin

My half baked attempt at a cutoff was to weld a short rod across the bolt (a wingbolt of sorts) securing the ground strap to the frame (just behind the seat in this case), so it can be unscrewed by hand in a few seconds.

Jud.Good day to you. I have mounted a cut- off
switch on the steering column under the dash.
A cable( same as starter cable) from + pole on the battery to the switch and then to the tube
Easy to reach. Procedure when stopping
Key off cut-off swich off. Then I can go out
of the car

Fhoralf. Norway TD 4490
Thoralf Sorensen (TD4490)


FWIW here is my cut off. You can operate it while sitting in the car. I use it all the time just as insurance.

The other switch controls which fuel pump to use or none.


PS: Don't make fun of the ugly glove box. I have since improved it.

Mort Resnicoff (50 TD-Mobius)

Mort, When my TD looks and runs as good as your I'll think about making fun of you but probably still won't. Thanks to everybody on this bbs for their help.
J K Chapin

This thread was discussed between 05/07/2013 and 06/07/2013

MG TD TF 1500 index

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