Toyota Repair: Backup Lights Dont Work, toyota camry, short circuits

Question
Its a 1992 Toyota Camry, w/ an automatic transmission. It has a lot of miles, i don't know the exact amount offhand. My backup lights don't work though. I discovered this after recently buying it, and having to replace several bulbs, including the brake lights, and when checking the lights, found those lights don't work. Naturally, I replaced the bulbs, even though they looked alright, and the lights still don't work. The Warning light that came on to tell me the other lights were out is not coming on, however. I took it in to have it looked at, and the place I took it too had no idea what was wrong with it, leading me to believe it is probably not the switch. Any ideas whats wrong with it before I take it to the dealer and have them look at it? Thanks!

Answer
It may be a wiring problem in the wire harness that runs along the left trunk hinge, the insulation should be cut open to check the wires inside the harness for short circuits and broken wires, there is also a relay behind the carpets on the left side which is known to burn out, have it checked for this at the dealer.