Originally Posted by Squishy!
Also check the harness where it bends at the trunk lid.
I've had two shorts in the bendy parts of harnesses and they were inside the loom. The wire insulation had gotten brittle from age, and the constant movement caused them to crack and short, except it was impossible to see since it was all wrapped up.
I would start at the back of the car and work forward. But where things are exposed or move, pull back the loom/tape and inspect.