Toyota Repair: 96 Camry cluster warning Light for taillight - always on. Huh?, broken wires, warning light

Question
96 Camry LE, 146K mi, 2.2L. The instrument cluster warning light comes on intermittently indicating that there's a light out somewhere in the back. However, *ALL* the lights are good and working! I've noticed that when I start the car - the warning light does NOT come on; however step on the brake (to put car in reverse) the warning light comes on about 90% of the time and stays on. A local shop (not a toyota dealer) put in a new harness in back (I assume they spliced it somewhere)- that fixed it for a while; after about 6 months the warning light was on again. They put in the new harness as the old one was corroded supposedly, and in fact I WAS burning out bulbs on the right hand side there fairly regularly - once a year or so. (I drive with lights on at all times) Last time they tried to fix this, they just removed the working bulb (right side), put in a new bulb - and THAT turned off the warning light for about 2 weeks. The toyota dealer tells me that there might be cracked/broken wires in the harness at the trunk hinge, but that makes no sense to me: if that were the case, none of the lights in the tail-light cluster(s) would work, right?  Any chance there's a sticking switch associated with the brake pedal thats making the warning light come on??   Other than that, car runs like a top!

Answer
There are a few reasons that causes this, first of all the problem is in the brake light circuit since when applying the brakes the light is turning on, the brake and tail lights are on seperate circuits so it is possible that there may be broken wires again, secondly, this may be caused by a malfunction in the tail light failure relay located inside the trunk on the left under the carpeting, lastly, even though all bulbs may look ok and work there may still have a problem, the warning light system works on reading the resistances of the bulbs and wiring, check or just replace all the bulbs and be sure to check the white/black ground wires on the bulb holders, these connections can become loose, check all the bulb sockets for excessive wear of the contacts.