Circuit Description
WARNING: This page is about a different car, the 2003 GMC Safari and 2003 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) monitors the voltage and controls the ground of the courtesy lamp relay on the courtesy lamp relay coil control circuit. When the BCM receives a signal from a door jamb switch, a signal to unlock the doors from the remote control door lock receiver module or the dome lamp switch being turned ON, the BCM will ground the relay and turn ON the courtesy lamps.