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MG MGA - brake lights

Thanks again to Barney's sight which is helping me daily. I am having a problem chasing down electrical problems. Now it is the brake lights and I suspect possibly a multiple of causes. First I have power at the green post of the brake switch and none on the green/purple post when the brakes are applied. So, when I jump the two terminals, I still get no brakelights but I get a quick buildup of heat at the connectors and at the tail lights. That would seem to indicate a ground fault. When the switch is jumped I get power at terminal 5 and at terminals 3 and 7 on the relay box. What's going on? If I am not getting power at the switch post, how can I get power at the relay box term. 5, 3 and 7?
David Holmes

Power in but no power out of brake switch with brakes applied indicates a bad switch.

If jumpering the brake switch gives power on 3,5,7 on the relay, then you also have power on the output terminal of the brake switch (because that's where it comes from to go to the relay). This sounds like you have good wiring up to the relay and through the normally closed contacts.

Wire heating indicates a ground short. Heating of a single connector terminal is usually a bad contact between wire and terminal, and the high resistance joint is causing the heating.

Start by disconnecting wires from tail lamps. Use a jumper wire to apply power (also ground if necessary) to test and verify operation of the lamp fixture. Eliminate any ground fault short in the lamp fixture and be sure it works properly before fussing too much with the rest of the wiring.
Barney Gaylord

This thread was discussed on 07/08/2006

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