Q: How do I diagnose and replace the back-up light switch for the Nissan Pathfinder?A: The back-up light switch is located on the right side of the transmission case. Check the back-up light fuse first. Raise the vehicle and unplug the switch's electrical connector to check for continuity. If voltage is present, trace the circuit between the connector and the bulbs for an open circuit. To replace the switch, unscrew it, apply sealant or tape to the threads, install it, plug in the connector and check the lights.