Headlamp Switch Operation
WARNING: This page is about a different car, the 2008 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
When the headlamp switch is placed in the ON position, ground is applied to the BCM through the headlamp switch headlamps ON signal circuit. The BCM then applies a ground to the headlamp low beam relay control circuit. This energizes the LO BEAM PCB relay and applies voltage through the headlamp LO BEAM fuses to the headlamps assemblies.