how do i find a ground wire short in a tail light?
The best tool I have found for this is called a power probe. You can however trace an issue like this with your average probe light. Turn your head lights on and stick the probe into the socket with the other end grounded to bare steel on the body. If the probe lights up then your tail light socket ground is bad. If not continue using the probe to test the wire back till you find the physical problem.
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