For 1990-2009 cars

## Headlights Circuit Description Domestic

### Headlamps

Battery voltage is applied to the headlamp switch continuously through CKT 2340. Voltage is applied to the headlamp dimmer switch and to the daytime running lamps (DRL) control module through CKT 10, when the headlamp switch is in the HEAD position. When the daytime running lamp (DRL) control module receives voltage on CKT 10, it disengages the DRL function. Battery voltage is applied to the low beam headlamps through CKT 12 when the headlamp dimmer switch is placed in the LOW position. Battery voltage is applied to the high beam headlamps and to the high beam indicator in the instrument cluster when the headlamp dimmer switch is placed in the HIGH position.

### Daytime Running Lamps (DRL)

The DRL control module is designed to automatically operate the exterior lights depending on the outside light conditions.

The DRL control module operates in the following 2 modes:

• | The day mode

| In the day mode, the DRL ambient light sensor senses daylight then the DRL control module activates the front turn lamps (non-flashing) under the following conditions:

• | The ignition is in RUN.

• | The headlamps are OFF.

• | The park brake is OFF.

• | The night mode

| In the night mode, the DRL ambient light sensor senses darkness turning off the front turn lamps and turning on the headlamps through CKT 10.

| Also in the night mode, the DRL ambient light sensor activates the following lamps through CKT 9:

• | The park lamps

• | The side marker lamps

• | The license lamps

• | The tail lamps

• | Voltage is also fed back through CKT 9 to the headlamp switch assembly to control IP dimming.

If the engine should stall with the DRL control module in the night mode, the DRL control module will turn off the headlamps, leaving the side marker, park, license and tail lamps in the ON position while the engine is being cranked. The headlamp and instrument panel lamp dimmer switch operate as usual.

The DRL control module receives voltage from the DRL Fuse through CKT 1839 and the HVAC/DRL Fuse through CKT 241. The park lamps and/or the headlamps may be operated manually at any time by using the headlamp and the instrument panel (IP) lamp dimmer switch. The DRL module will not operate if the system voltage is less than 9 volts or greater than 18 volts.

### Daytime Running Lamps (DRL) Ambient Light Sensor Input

The DRL ambient light sensor is a light sensitive variable resistor. Its resistance decreases as the outside light intensity increases. The DRL control module measures the voltage drop across the DRL ambient light sensor and determines whether it should operate in the day or the night mode.

### Park Brake Input

The DRL control module will not operate any headlamps or exterior lamps if the park brake is applied before the ignition switch is turned to the RUN position. This allows the operator to start the vehicle and keep the headlamps off, as long as the park brake is applied. The DRL control module will activate the headlamps when the park brake is released with the ignition switch in the RUN position. This feature will only function when the park brake is applied before the ignition switch is turned to the RUN position. The headlamps will not turn off if the park brake is applied after the ignition switch is turned to the RUN position.

## Headlights Circuit Description Export

### Headlamps Circuit Operation -- Export

When the Headlamp and I/P Lamp Dimmer Switch is moved to the HEAD position, battery voltage is supplied through circuit 10 to the Headlamp Dimmer Switch. The Headlamp Dimmer Switch supplies voltage to the high beam lamps and the low beam lamps. When the dimmer switch is in the Low position, battery voltage is applied through circuit 12 to the fuse block to power the LH and RH HEAD LP LOW Fuses. The fuses then feed battery voltage through circuits 312 and 712 through the Underhood Electrical Center to the RH and LH Headlamp Low beam filaments.

When the Headlamp Dimmer switch is in the High position, battery voltage is applied through circuit 11 to the High Beam Indicator and to the fuse block to power the LH and RH HEAD LP HIGH Fuses. The fuses then feed battery voltage through circuits 311 and 711, through the Underhood Electrical Center to the RH and LH Headlamp High beam filaments.

For the Flash to Pass feature, batttery voltage is applied from circuit 2340 through the headlamp dimmer switch to circuit 11 to illuminate the high beam headlamps and indicator.

### Daytime Running Lamps (DRL) -- Export

The DRL control module is designed to automatically operate the exterior lights when the engine is running. The DRL control module activates the low beam headlamps and tail lamps under the following conditions:

• | The engine is running.

• | The park lamps are OFF.

The DRL control module receives voltage from the Park Lamp Fuse through CKT 1340 and the HVAC/DRL Fuse through CKT 241. The park lamps and/or the headlamps may be operated manually at any time by using the headlamp and the instrument panel (IP) lamp dimmer switch. The DRL module will not operate if the system voltage is less than 9 volts or greater than 18 volts.

### Engine Oil Pressure Indicator Switch

The DRL control module uses the Engine Oil Pressure Indicator Switch to control operation of the low beam headlamps and exterior lamps during the vehicle start up cycle. After the vehicle is running and the engine oil pressure increases, the Engine Oil Pressure Indicator Switch will open signaling the DRL control module to activate the headlamps.