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MG MGA - Hot (physically) Ignition Switch

Started up my 1500 the other day and noticed smoke coming out from the dash. Snooped around and discovered the wires attached to the ignition switch are getting very hot.
I know my wiring isn't totally correct because the headlights and parking lights do not come on unless I have the ignition on, but that's the way the car was when I bought it many years ago and haave not had problems with the wiring.
What could have changed to cause this? HOw do I track down this gremlin?
Steven B

Most probably bad contacts at the terminals. Several wires into one hole. I used separate terminal strips to avoid this.
Art Pearse

Thanks Art, I just have two wires to the switch, a red and a black, but I know this is an aftermarket wire harness.
What is confusing is that it has been fine for 10+ years.
Steven B

Headlights and parking lights should definitely NOT go through the ignition switch.
Barney Gaylord

Had the same thing happen on my Jaguar. I noticed that occasionally the switch was hot (same switch). One day it didn't start because the internal contacts had finally burnt out. Of course that day had to be during the biggest car show in the county as I was just waiting to go into the centre ring! After a bit of fumbling around I expect I was the only car in there that was hotwired!
Neil MG

I agree with all comments but particularly Barney's as the current taken by the headlights is far higher than anything that should go through the ignition switch. If you want to carry on with this arrangement you could do it by fitting a relay.

Paul
Paul Dean

Thanks, maybe it has been hot all along and I just never noticed it. I'll have to track my wires and get things sorted - with the assistance of Barney's great wiring charts!
Steven B

Does the switch only get hot when the lights are on? If not, and it gets hot always, then I would think you have a problem with the contacts in the ignition switch.
Not to say, that the lights should not be controlled by the key, and that may have created the problem with the contacts?
g Victors

Well - I am not sure where the harness came from, but it has one 14 gauge red wire going to one pole of the ignition switch and the other pole goes to ground. Anyone aware of aftermarket harnesses that were not wired the same as the originals?
How on earth would I sort this out to get the lighting circuit separate from the ignition circuit like it should be?!?!?!?
Steven B

Diagram here: http://mgaguru.com/mgtech/electric/circ_d.htm

Disconnect all wires from ignition switch and lighting switch,and start over, one wire at a time. If wire colors are incorrect you will need an ohm meter or a continuity tester (or test light with power source) to find opposite ends of each wire.
Barney Gaylord

Thanks Barney -
Your diagrams have been a great help and I decided last night that I would have to do what you suggest. Just wish I knew this issue when I had the dash out for painting, it is such a PITA to get under there. Also, since the one wire to the ignition switch comes out of part of the harness, I will probably have to abandon a wire or two and do some direct replacements - hopefully without shorting anything!
Steven B

This thread was discussed between 21/07/2014 and 28/07/2014

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