For 1990-2009 cars

## Headlights Circuit Description Buick

Battery positive voltage (B+) is supplied at all times to the lamp control module (LCM) through the LH underhood fuse block LCM/HDLP circuit breaker via CKT 242 (RED). When the headlamp switch is placed in the ON position, the headlamp switch input to the LCM is grounded via CKT 103 (WHT). The LCM then supplies battery positive voltage (B+) via CKT 12 (TAN) to the following components:

• | Left low beam headlamp

• | Right low beam headlamp

When the headlamp dimmer switch is placed in the HIGH position, the LCM removes battery positive voltage (B+) from the low beam headlamps. The LCM supplies battery positive voltage (B+) via CKT 11 (LT GRN) to the following components:

• | Left high beam headlamp

• | Right high beam headlamp

The LCM provides battery positive voltage (B+) to the appropriate headlamps under the following conditions:

• | The ignition switch is in the RUN position.

• | The ambient light sensor indicates darkness.

The lamp control module (LCM) monitors the ambient light conditions through the ambient light sensor. The ambient light sensor is a variable resistor whose resistance changes as the surrounding ambient light level changes. As the ambient light decreases, the resistance of the ambient light sensor increases. The LCM measures the resistance across the ambient light sensor and determines whether it is day or night.

## Headlights Circuit Description Oldsmobile

Battery positive voltage (B+) is supplied through the LH underhood fuse block LCM/HDLP circuit breaker via CKT 242 (RED) at all times to the following components:

• | Headlamp switch

• | Lamp control module (LCM)

• | Switch of the RH IP fuse block headlamp relay position J

When the headlamp switch is placed in the ON position, battery positive voltage (B+) is supplied via CKT 10 (YEL) to the coil of the headlamp relay position J. The coil is permanently grounded to G201 via CKT 1450 (BLK). The coil is energized and the contacts close providing battery positive voltage (B+) to the headlamp dimmer switch via CKT 1346 (LT BLU). When the headlamp dimmer switch is in the LOW position, battery positive voltage (B+) is supplied via CKT 12 (TAN) to the following components:

• | Left low beam headlamp

• | Right low beam headlamp

When the headlamp dimmer switch is in the HIGH position, battery positive voltage (B+) is supplied via CKT 11 (LT GRN) to the following components:

• | Left high beam headlamp

• | Right high beam headlamp

The LCM provides battery positive voltage (B+) via CKT 1346 (LT BLU) through the headlamp dimmer switch to the headlamps under the following conditions:

• | The ignition switch is in the RUN position.

• | The ambient light sensor indicates darkness.

The lamp control module (LCM) monitors the ambient light conditions through the ambient light sensor. The ambient light sensor is a variable resistor whose resistance changes as the surrounding ambient light level changes. As the ambient light decreases, the resistance of the ambient light sensor increases. The LCM measures the resistance across the ambient light sensor and determines whether it is day or night.

## Headlights Circuit Description Pontiac

Battery positive voltage (B+) is supplied at all times through the LH underhood fuse block LCM/HDLP circuit breaker via CKT 242 (RED) to the following components:

• | Headlamp switch

• | Lamp control module (LCM)

When the headlamp switch is placed in the ON position, battery positive voltage (B+) is supplied via CKT 10 (YEL) to the headlamp dimmer switch. When the headlamp dimmer switch is placed in the LOW position, battery positive voltage (B+) is supplied via CKT 12 (TAN) to the following components:

• | Left low beam headlamp

• | Right low beam headlamp

When the headlamp dimmer switch is in the HIGH position, battery positive voltage (B+) is supplied via CKT 11 (LT GRN) to the following components:

• | Left high beam headlamp

• | Right high beam headlamp

The LCM provides battery positive voltage (B+) via CKT 12 (TAN) to the headlamps under the following conditions:

• | The ignition switch is in the RUN position.

• | The ambient light sensor indicates darkness.

When equipped with lamp monitoring, the headlamp battery positive voltage (B+) feeds pass through the adaptive lamp monitor control module to the headlamps. The low beam headlamps receive battery positive voltage (B+) through CKT 1312 (TAN or TAN/WHT). The high beam headlamps receive battery positive voltage (B+) through CKT 1311 (LT GRN, LT GRN/BLK or LT GRN/WHT)

The lamp control module (LCM) monitors the ambient light conditions through the ambient light sensor. The ambient light sensor is a variable resistor whose resistance changes as the surrounding ambient light level changes. As the ambient light decreases, the resistance of the ambient light sensor increases. The LCM measures the resistance across the ambient light sensor and determines whether it is day or night.

## Headlights Circuit Description Perimeter Lighting (Buick)

Perimeter lighting provides a personal security feature. The perimeter lighting feature illuminates all exterior lights on the vehicle for 15 seconds when the keyless entry transmitter is used to unlock the doors and it is dark outside.

The perimeter lighting system uses the following lamps:

• | The backup lamps

• | The headlamps

• | The park lamps

• | The cornering lamps

When you press the UNLOCK button on the keyless entry transmitter, the remote function actuator (RFA) module grounds CKT 624 (BLK/WHT) to the lamp control module (LCM). The LCM then provides battery positive voltage (B+) to the following components:

• | The headlamps

• | The park lamps

Battery positive voltage (B+) is supplied at all times through the IP fuse block PERIMETER LT fuse 8A via CKT 1654 (TAN) to the perimeter lighting relay. The RFA provides ground for the perimeter lighting relay via CKT 1655 (DK GRN). The coil is energized. The switch contacts close. Battery positive voltage (B+) is provided to the following components:

• | Backup lamps

• | Cornering lamps (if equipped)

Refer to the following items for additional perimeter lighting schematics:

• | Exterior Lights Schematics

• | Backup Lamp Schematics