Backup Lamps (Regal)
WARNING: This page is about a different car, the 2002 Buick Regal and 2002 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The backup lamps are located in the rear compartment lid applique. The backup lamps operate when the ignition switch is in the RUN position and the transaxle range selector lever is in REVERSE.
The R/CMPT REL fuse supplies battery voltage at all the times to the coil side and the switched side of the backup relay. When the vehicle is placed in REVERSE, a class 2 signal is sent to the BCM. The BCM then applies a ground through the backup lamp relay coil control circuit to the backup lamps relay. This energizes the relay and allows battery voltage to be applied to the backup lamps turning them on. The backup lamps receive a constant ground signal