Switch is on the tranny... blue plug. Have you disconnected the trunk harness and ohm'd it out yet? After 12-13 years of bending over a hinge sometimes a wire just breaks.. I personally would start there since its free 
yep!!! harness was severed at the hinge. However, I repaired all the wires and the revers lights are still not workingI agree most of the time it is that harness
OK after peeling the brittle hardened rubber tubing off I found a total of 10 broken wires LOL i used some corrugated wire tubing and alot of wire crimps with the built in heatshrink. The whole trunk lights up again as it should and the reverse lights work..sheeshyep!!! harness was severed at the hinge. However, I repaired all the wires and the revers lights are still not working