When the ignition switch is in the RUN position, voltage is available at the backup lamp switch from the B/U circuit breaker through CKT 41 (BRN). The backup lamp switch is on the transmission. When the transmission is in Reverse, the backup lamp switch contacts close. The closed switch applies voltage through CKT 24 (LT GRN) to the upfitter connector terminal K. The body builder provides the necessary wiring inside the vehicle to the rear lamps and the ground provisions for the backup lamps.