Circuit/System Description
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The front fog lamp switch signal circuit is referenced from battery voltage by the BCM. When the fog lamp switch is activated, the signal circuit is grounded through the switch and the signal circuit voltage goes low. The BCM controls the front fog lamps through the fog lamp relay in the underhood fuse block. Battery voltage is supplied to the relay coil and switch, and the BCM energizes the relay by grounding the fog lamp relay control circuit.