Circuit/System Description
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 GMC Yukon XL, 2011 GMC Yukon, 2011 Chevrolet Tahoe, 2011 Chevrolet Suburban, and 2011 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
When the Headlamp and Panel Dimmer Switch is placed in the headlamp ON position, ground is applied to the body control module (BCM) through the headlamp low beam signal circuit. The BCM then applies ground to the HDLP LO/HID Relay control circuit which energizes the low beam relay. With the low beam relay energized, the switch contacts close allowing B+ to flow through the LOW HDLP fuses to the low beam headlamps.