Headlamp Switch Operation
WARNING: This page is about a different car, the 2006 Buick Lucerne. 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 through the headlamp switch headlamps On signal circuit to the BCM. The BCM then applies a ground through the headlamp low beam relay control circuit. This energizes the LO BEAM PCB Relay and voltage is applied through the switch side of the relay and both low beam headlamp fuses to the low beam headlamps.