There is no reverse lamp switch on these trucks. The Transmission Range Sensor, which is internal to the transmission, is used to determine when the shifter has been placed in reverse. That information is then networked to the Body Control Module (BCM) which turns on the reverse lamps. There is no fuse, the circuit is operated by a transistor.
The first thing to determine is whether the range signal is coming from the transmission. Does the indicator in the instrument cluster show R when reverse is selected? Do the camera and backup sensors work? If so, the range signal is valid and the issue is network, BCM, or circuit related. Start by checking for any aftermarket wiring tied into the reverse lamp circuits and verifying that the bulbs are factory spec. The BCM monitors amperage draw; if it’s above or below threshold, it will disable the circuit output.
