1993 Nissan Pathfinder reverse light failure

Help My reverse lights won't work! I have replaced the switches on the trany, the light bulbs, the fuse, what else would cause them to not work. The switches where taken out and tested also. They both allow current. The wires to the switches appear to have current going thru them (test light tested) They were working after the initail repair and then poof!... not any more...Have a ghost, can't find 'em