Circuit/System Description
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Ground is applied at all times to the CHMSL relay coil. Upon brake activation, the body control module (BCM) applies voltage to the CHMSL relay control circuit to the coil side of the relay, energizing the relay. Battery voltage is then applied through the switch side of the relay, the CHMSL fuse, and the CHMSL control circuit to the center high mounted stop lamp (CHMSL). The CHMSL is grounded at G 200.