The headlamps are controlled by the body control module (PZM). The battery positive voltage (B+) is applied at all times through the HDLPS fuse at the switch side of the headlamp relay via CKT 340 (ORN).

Battery positive voltage (B+) is also applied at all times through the RADIO/PHONE fuse to the coil side of the high/low beam headlight relay via CKT 40 (ORN/BLK). Both relays are controlled by the PZM at separate output cavities.

When the headlamp switch is in the HEAD position, the instrument cluster headlamp switch input is grounded through CKT 10 (YEL) and the headlamp switch. The instrument cluster sends a request through the Class 2 serial data line to the PZM in order to active the low beam headlamps. The PZM supplies positive battery voltage (B +) to the coil side of the headlamp relay via CKT 352 (WHT). The coil receives ground through the headlamp switch via CKT 10 (YEL). The coil of the headlamp relay is then energized, closing the switch contacts. Battery positive voltage (B +) is then applied through the high/low beam headlamp relay via CKT 1346 (LT BLU) and the L HDLP LO fuse and R HDLP LO fuse via CKT  12 (TAN) to the left and the right low beam headlamps respectively.

High beam operation is enabled by pulling the multi-function lever (the turn signal lever) toward the driver. The headlamp system changes state to the high beams if the low beams are already on. If the low beams are not on, and the ignition is in the RUN position, the high beams illuminate for as long as the malfunction lever is pulled and held inward (flash-to-pass position).

When the multifunction lever is pulled inward, the headlight dimmer switch closes, supplying battery positive voltage (B+) to the instrument cluster high beams/flash-to-pass input. In response to this input, the instrument cluster sends a request via the Class 2 serial data line to the PZM to activate the high beam headlamps. The PZM provides a ground for the coil of the high/low beam headlamp relay via CKT  1969 (BLK/WHT). The coil is then energized causing the switch contacts to close and apply battery positive voltage (B+) via CKT 11 (LT GRN) through the L HDLP HI fuse and R HDLP HI fuse to the left and the right headlamps respectively. The Eldorado right high beam headlamp is grounded to G101. The left high beam headlamp receives ground through the DRL relay from G101. The Deville high beam headlamps are both grounded to G101. When the switch contacts of the high/low beam headlamp relay close, battery positive voltage (B+) is removed from the low beam headlamps causing them to turn off when the high beam headlamps are on.

The instrument cluster monitors the ambient light conditions through the ambient light sensor via CKT 278 (WHT). The ambient light sensor is a variable resistor. The sensor's resistance changes as the as the ambient light level changes. As the ambient light decreases, the resistance of the ambient light sensor increases. The value of the input voltage is between 0 and 5 volts. The voltage level at the instrument cluster light sensor increases as the ambient light sensor resistance increases.

The wiper activated headlamp function allows the headlamps and the park lamps to be activated by the windshield wipers. For this to occur, the ignition switch must be in the RUN position. The twilight sentinel must be enabled. The windshield wiper switch must be activated for approximately 20 seconds. The instrument cluster receives a signal at the wiper ON input through CKT 91 (GRY) when the windshield wipers are activated for approximately 20 seconds. In response to this input, the instrument cluster sends a request via the Class 2 serial data line to the PZM to activate the headlamps and the park lamps.

The wiper activated headlamp feature can be disabled by either turning the windshield wiper switch off, the twilight sentinel off, or the ignition switch to the OFF position. The wiper activated headlamp feature will be disabled, if any of these conditions occur. The wiper activated headlamp feature will override the daytime running lamps (DRL), if active.