Circuit Operation

HEADLAMP OPERATION
Battery voltage is applied through the RH Rear Power Distribution Center MaxiFuse Block HEADLAMP Circuit Breaker at all times. The circuit breaker will open if the headlamp circuit draws too much current. When the circuit breaker opens, it interrupts the current flow. With no current flow, the circuit breaker cools and resets automatically. With the Headlamp Switch in HEAD, voltage is applied from the Lamp Control Module through the Headlamp Dimmer Switch to the LH and RH Low Beam Headlamps. High beam operation is enabled by pulling the Multi-Function Lever (turn signal) towards the driver. Voltage is then applied from the Lamp Control Module through the Headlamp Dimmer Switch to the LH and RH High Beam Headlamps.

FLASH-TO-PASS
For Oldsmobile, battery voltage is applied through the Engine Compartment MaxiFuse� Block FOG LAMPS Fuse at all times to the Headlamp Dimmer Switch. For Buick, battery voltage is applied through the Engine Compartment MaxiFuse� Block FLASH TO PASS Fuse at all times to the Headlamp Dimmer Switch. When the Multi-Function (turn signal) Lever is pulled towards the driver, voltage is applied through CKT 42 and the Headlamp Dimmer Switch to the LH and RH High Beam Headlamps. If the headlamps are off, pulling the lever will turn the high beam headlamps on for as long as you hold the lever. Releasing the lever will turn the headlamps off. If the low beam headlamps are on when the lever is pulled, the low beams will shift to high beams and remain there until the lever is pulled again. If the high beam headlamps are on when the lever is pulled, the high beams will shift to low beams and remain there until the lever is pulled again.

TWILIGHT SENTINEL
Twilight Sentinel keeps the lamps on for a delay period (0 to 180 seconds) when the Twilight Sentinel Switch is ON, the vehicle is in PARK, the Ambient Light Sensor indicates darkness and the Ignition Switch is OFF. The Twilight Sentinel feature does not affect the operation of the Daytime Running Lamps.

AMBIENT LIGHT SENSOR
The Lamp Control Module monitors ambient light conditions through the Ambient Light Sensor. The Ambient Light Sensor is a variable resistor whose resistance changes as the ambient light level around it changes. As ambient light decreases, the resistance of the Ambient Light Sensor increases. The Lamp Control Module measures the voltage across the Ambient Light Sensor and determines whether it is day or night.

DAYTIME RUNNING LAMPS (DRL)
When the Ignition Switch is in RUN, the Ambient Light Sensor indicates daylight and the vehicle is not in PARK, the Daytime Running Lamps are activated. When these conditions have been met, voltage is applied from the Lamp Control Module through the Daytime Running Lamps Resistor to the low beam headlamps. The voltage drop across the Daytime Running Lamps Resistor causes the low beam headlamps to light at a reduced intensity. The Daytime Running Lamps are disabled if the high beam headlamps are on or if the vehicle is placed in PARK. When the Ambient Light Sensor indicates darkness, the low beams are automatically switched to regular intensity.

FOG LAMPS (OLDSMOBILE ONLY)
With the Headlamp Switch in HEAD or PARK, voltage is applied through I/P Fuse Block INT LP Fuse to the Fog Lamp Switch. Voltage is applied at all times through Engine Compartment MaxiFuse� Block FOG LAMPS Fuse to the switch side of the Fog Lamp Enable Relay. When the Fog Lamp Switch is ON, voltage is applied to the coil of the Fog Lamp Enable Relay. The coil receives ground through the Lamp Control Module. With the Fog Lamp Enable Relay coil energized, its contacts close applying voltage to the fog lamps. If the high beam headlamps are turned on, the Lamp Control Module removes the ground from the Fog Lamp Enable Relay and the fog lamps turn off.