GM luxury vehicles use a system called Twilight Sentinel. The twilight delay switch in the headlamp switch assembly is supplied a 5 volt reference from the instrument panel integration module (IPM) as shown in below schematic.
GM Twilight Sentinel Circuit and Wiring Diagram
The IPM also provides ground to the twilight delay switch. The switch is a potentiometer in which the resistance varies as the switch is moved. The IPM receives an input voltage proportional to the resistance of the potentiometer through the twilight delay signal circuit. The IPM sends a class 2 message to the dash integration module (DIM) indicating the on/off status and delay length for the twilight sentinel.
With the twilight sentinel switch in any position other than OFF, the DIM will turn the headlamps on or off according to the daytime/nighttime status sent by the IPM. The
DIM uses the twilight delay signal in order to keep the headlamps and park lamps on after the ignition switch transitions from ON to OFF during nighttime conditions.