Headlamp: Description and Operation

CAUTION:
- Halogen bulbs contain a gas under pressure. Handling a bulb improperly could cause it to shatter into flying glass fragments. To help avoid personal injury:
- Turn OFF the headlamp switch and allow bulb to cool before changing bulbs. Leave the switch off until bulb change is complete.
- Always wear eye protection when changing a halogen bulb. Handle the bulb only by its base. Avoid touching the glass.
- Do not drop or scratch the bulb. Keep moisture away.
- Place the used bulb in the new bulb's carton and dispose of it properly. Keep halogen bulbs out of reach of children.

HEADLAMPS
Battery voltage is applied to the headlamp switch at all times through circuit 2340. When the headlamp switch is in the HEAD position, voltage is applied to headlamp dimmer switch and to the DRL control module through circuit 10. When the DRL control module receives voltage on circuit 10, it disengages the DRL function. When the headlamp dimmer switch is placed in the LOW position, battery voltage is applied to the low beam headlamps through circuit 12. When the headlamp dimmer switch is placed in the HIGH position, battery voltage is applied to the high beam headlamps and to the high beam indicator in the instrument cluster.

DAYTIME RUNNING LAMPS (DRL)
The Daytime Running Lamps (DRL) control module is designed to automatically operate exterior lights depending on outside light conditions. The DRL control module operates in two modes: the day mode and the night mode. In the day mode, the DRL ambient light sensor senses daylight then the DRL control module turns on the front turn lamps (non-flashing) under the following conditions:
- The ignition is in RUN.
- The headlamps are off.
- The park brake is OFF.

In the night mode, the DRL ambient light sensor senses darkness then turns off the front turn lamps and turns on the headlamps through circuit 10 and turns on the park, side marker, license, and tail lamps through circuit 9. If the engine should stall with the DRL control module in the night mode, the DRL control module will turn off the headlamps and leave the side marker, park, license and tail lamps are on while the engine is being cranked. The headlamp and instrument panel lamp dimmer switch operates as usual. The DRL control module receives voltage from the DRL Fuse through circuit 1839 and the HVAC/DRL Fuse through circuit 241. The park lamps and/or the headlamps may be operated manually at any time by using the headlamp and instrument panel lamp dimmer switch. The DRL module will not operate if the system voltage is less then 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 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 mode or night mode.

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