240/91 backup lamps do not work...

Is the switch completing the circuit?

1. check bulbs with test meter.
2. check switch with meter.
3. check wiring harness end to end.
4. check fuses or relays.

if all this fails....

reconnect the battery!

240 reverse lights are powered through an edge connector at the left rear taillight assembly. The connector contacts copper strips fused to a mylar "wiring plate." Over time the compression forces of the connector cause the plastic under the mylar bit to creep and deform. Once that happens the edge connector cannot make adequate contact to complete the circuit to the bulbs. Often using a piece of brass shim stock to bridge the connection on the black wires in the edge connector will restore connectivity to the bulbs. (One black wire comes from the switch and the other goes to the bulb on the other side of the car after being bridged at the connector.)

Bob