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MG TD TF 1500 - Lightswitch; trouble shooting

I have a TD. When I switch on my sidelights and taillights, they work. When I depress the brake pedal, my brake lights come on. When I switch on my headlights, they work. However, when I turn on my headlights, my sidelights and taillights do not come on. I have checked for loose wires on my light switch and they all seem tight. I want to check to see if my light switch is bad. I have a volt ohm meter. Is there some way to test my light switch to see if it is OK?
Milt
Milton Babirak

Tail and side lights should be connected to ignition switch terminal T with a red cable.

Headlights should be connected to ignition switch terminal H with a blue cable.


Laurent.
LC Laurent31

Milt, Laurent hit on the nose. Look at the wiring diagram in the WSM. Your wires are on the contacts of the switch. What your VOM should show you (switch removed) is that there is contact between terminal A and terminal T when the switch is in the sidelight/taillight position. When it is in the headlight position there is contact between terminals A and T and H. With the switch in the car with power - your VOM should show voltage (to ground) on terminal T (only) in the sidelights position and voltage on both terminals T and H in the headlights position. Bud
Bud Krueger

Bud and Laurent.
Thanks you for your comments. They were very helpful.
I checked the switch as suggested and there was voltage to the T terminal when the sidelights were on. There was voltage to the H terminal when the headlights were on but there was no voltage to the T terminal when the headlights were on. From this, I surmise that the switch is bad.
Any thoughts?
If I have to replace the switch, I can buy a new one from Moss. This does not look easy since the switch appears to be secured to the back of the dash by a wire clip on the back of the switch. There seems to be very little room to work.
Milton
Milton Babirak

Milt, I'd try a shot of contact cleaner first, just to be safe. It might clear up the problem. Bud
Bud Krueger

You can open it to clean. But it is very tricky to get everything back and aligned. Because of springs and the number of parts you would need a dozen of hands.
Or, many time and patience.

Try contact cleaner while assembled first.

Laurent.
LC Laurent31

I can spray the terminals but they seem clean. None of that blue green powder from oxidation.
I am not sure what kind of cleaner you use. I usually spray contacts with WD-40 and that seems to work. If you have something specific in mind, please let me know.
The gentlemen who sold me the switch is willing to repair it. So, I had planned on removing it from the dash and mailing it to him if this contact cleaner doesn't work. It looks like it is not going to be easy to remove it from the dash and even harder to reinstall it. If you have any thoughts to make the removal and reinstallation any easier, they would be welcomed.
Milton Babirak

That wire holding it in is like a "C" clip. Just pull it to one side. That's all that holds it in place.
Just remove the power before you do this. ( battery terminal ) .

M Grogan

Not WD-40, Milt. The generic product is called 'contact cleaner'. You'll try to spray it inside of the switch so as to have it contact the contacts. Bud
Bud Krueger

I saw the wire clip. It looks like it completely surrounds the switch on the back side. Not a "C" clip but an "O" clip. It has a nut and bolt. Don't I have to loosen or remove the nut and bolt first? Looks like it would be difficult to get back on if I had to reinstall the switch.
Bud- Thanks. I'll go out and get some contact cleaner. No big deal. I did not know you could spray inside the switch.That might help. But I do not see any opening to spray inside. How do you do that? Where's the opening?
Milton Babirak

I don't know, Milt. If there isn't one, you're out of luck. Perhaps Peter Hehir would know. He has an article about the rebuilding of the switch. Perhaps he would share it with you/us. Bud
Bud Krueger

This thread was discussed between 05/03/2017 and 08/03/2017

MG TD TF 1500 index

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