Rear light positive wire?
 

Hey, I’m trying to instal an led exhaust tip but I can’t seem to find which right side rear light wire is positive.

I am installing it so when I turn on my lights at night it turns on the exhaust light too.

Thanks!

Which mustang are we talking about? 2018? 1967? 1978 II?

Although it might be helpful, the thing you could do is to take out a running light (I'm assuming you don't want brake lights to run that thing, right?), turn on the running lights on the switch, then test with a multimeter for which lead in the socket is the one you're looking for, as it should be the only +12V on at that time. Then go to town on whatever wiring job you're going to do. Another way is to use a test pin/needle and pierce the wires on the other side of the socket and test that way (being careful to not accidentally ground the thing of course), then use liquid electrical tape to seal the hole back up. Some examples:
Test pins: Liquid electrical tape:
Examples, NOT endorsements, mind.

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For me, I'd also be running a separate fused power line directly to the back from the battery, and use whatever signal I could grab that makes sense to trigger a relay to power the LED, and therefore not mess with the wiring of the running lights, but I'm a special kinda dummy like that. :) I'd just rather get the signal from a more central source than a tail lamp is all, say, from the light switch directly. Yes, it's more wiring, but I'd know I'd not interfere with the tail lights. Just some food for thought, I'm sure I'm over thinkin' it... But that same signal and power lines could be used for more things too, so...? :dunno:

Hope that helps, welcome to the forum, and good luck! :nice: :wave: