Circuit/System Description
WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
When the transmission range selector is placed in the REVERSE position, a signal is sent to the body control module (BCM). The BCM then applies voltage through the backup lamps relay control circuit energizing the backup lamps PCB relay. With the relay energized, battery voltage is applied through the left and right backup lamp fuses and the supply voltage circuits to the backup lamps. The engine may need to be running for the backup lamps to function.