First check the bulbs themselves. If they are good, check for power at the sockets. If you have power, check the ground. If you don't have power, there is a switch that I think is located on the outside of the tranny that closes when you shift into reverse which allows current to flow in the bulbs. Check for power to and from that switch. I don't have an electrical diagram so this might be easy or it might be a royal pain in the ass.