Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
The turn signal fuse powers the reverse light circuit. The reverse switch is built into the transmission range switch on the side of the transmission. The light green wire coming out of the switch runs to the reverse lights. Since the problem is intermittent, it may be harder to track down. My suggestion is to inspect the wiring near the transmission, near both taillight assemblies, and at the trailer wiring harness (may be routed above spare tire). Look for any signs of pinched wires or chafing of the harness, particularly the light green wire.
Harness is likely shifting around and shorting at some times and not at others. For that reason, looking at components that can move (transmission harness and trailer wiring harness) is where I would start the inspection.