Current is supplied from the B/U LP fuse to the back up lamp switch through CKT 839. When the switch closes, voltage is applied to the VEH B/U and TRLR via CKT 24. Voltage to the lamps is supplied on CKT 1324. CKT 1324 also supplies voltage to the HD trailer wiring connector and the automatic day-night mirror. For the LD trailer wiring, voltage is supplied from the VEH B/U fuse.