Circuit Description
WARNING: This page is about a different car, the 2002 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) turns on the automatic lighting control (ALC) headlamp relay when the ambient light sensor senses a dark condition. Battery positive voltage is supplied to the relay at all times through the LH HDLP fuse. The BCM grounds the ALC headlamp relay control circuit in order to activate the relay.