Circuit Operation

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) through circuits 14 and 15 if:
1. The ignition is in RUN.
2. The headlamps are OFF.
3. If 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 lit 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 headlamp and instrument panel lamp dimmer switch receives voltage from the HEADLAMP Circuit Breaker through circuit 2340. The park lamps receive voltage from the PARK I/P Fuse when the Headlamp and instrument panel lamp dimmer switch is in HEAD through circuit 1340. The DRL operation of the turn signals and the hazard flasher will operate normally. 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 then 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 turn lamps if it is daylight conditions outside. 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 turn lamps will not turn off.