Circuit/System Description
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The stop lamp switch is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a low reference signal and a B+ reference voltage to the stop lamp switch. When the stop lamp switch contacts close indicating the brakes have been applied, the BCM will apply battery voltage to stop lamp relay control circuit and the center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the STOP LP fuse to illuminate the left and right stop lamps.