Circuit/System Description
WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
When the BCM receives a signal to command the courtesy lamps ON, it applies battery voltage through the dome/courtesy lamps control circuit to the courtesy lamps. The door sill illumination receives voltage through the courtesy lamps circuit. The door sill illumination harness connector includes a power inverter which converts the battery voltage to 150 V AC (550 Hz). This AC voltage is supplied to the door sill lamps and causes them to illuminate.