65 gto a/c wiring
 

Hello, does anyone know what the extra ground prong on the 7 prong ignition switch is for?
Thanks, Paul

I'm going to guess that it's for the temp light?

I believe you're right about the temp light. IIRC, that ground post gets ground when the key is turned to start. This grounds out the temp light while the engine is cranking so you can see that the bulb works. Other lights[alt, oil] will come on with just the key on, engine off, but the temp light won't if the engine is not hot. So the only way to know if the bulb works is if something grounds it out while cranking. This is where the ground post on the ignition switch comes in.

This is easy to test with a 12 volt test light. Just hook the alligator clip of the test light to a 12 volt power source. Be sure the ignition switch is grounded. Then, with the key off, check that ground post on the switch to see if the test light lights up. It should not light up until, and only when, you turn the key to start. If this is how it works, then I would say it goes to the temp light.

Thank you for the help and info.
Thanks, Paul