Circuit/System Description
WARNING: This page is about a different car, the 2011 GMC Acadia, 2011 Chevrolet Traverse, and 2011 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
Battery voltage for the courtesy lamps is supplied at all times, from the INAD/PWR/LED Fuse located in the I/P fuse block to the body control module (BCM). When the BCM receives a signal to command the courtesy lamps ON, it then applies voltage through the courtesy lamps control circuits to the courtesy lamps.