No relay. Two wire switch on the top of the trans. Power goes in, and when reverse is engaged, the switch closes and completes the circuit to the lamps. Wiring comes through the floor and under the console then toward the dash under the ash tray/ fuse box. There should be 2 conectors. 1 for O/D, 1 for rev lights. Check the conectors at the switch, they may be loose. I think the rev. light switch is on the left side of trans, but not positive. There is a switch on each side, 1 has single wire/terminal, other has 2. Later is rev switch.