Headlamps With Daytime Running Lights

The LO Beam Headlamps are automatically controlled by the Daytime Running Lamps (DRL) Module. With sufficient ambient light (daylight), the DRL Module will activate the LO Beam Headlamps at a reduced intensity. With low light conditions, the DRL Module will activate the Park and Tail Lamps, and LO Beam Headlamps at full intensity. If the DRL System is inoperative, the Headlamp Switch overrides the DRL System to provide manual control of the Headlamps. If the Park Brake is set when the Ignition Switch is turned to "RUN," the DRL Module will not activate the LO Beam Headlamps until the Park Brake is released.

Battery voltage is applied at all times to the DRL Module through I/P Fuse #31 to power the Park and Tail Lamps. Voltage is applied to the DRL Module through I/P Fuse #20 to power the control circuitry of the DRL Module. Battery voltage is applied to the DRL Module through CKT 274 with the Headlamp Switch "OFF," to power the LO Beam Headlamps at reduced or full intensity.

As the intensity of light reaching the Headlamp Automatic Control Ambient Light Sensor decreases, the resistance of the Sensor increases. When the DRL Module senses a high resistance in the Sensor, the DRL Module de-energizes the internal DRL Relay and energizes the internal Head Relay. Battery voltage is applied through the closed contacts of the Head Relay to CKT 10. With the Headlamp Dimmer Switch in "LO," the LO Beam Headlamps are "ON" at full intensity. With the Dimmer Switch in "HI," the HI Beam Headlamps and Indicator are "ON."

As the intensity of light reaching the Sensor increases, the resistance of the Sensor decreases. When the DRL Module senses a low resistance in the Sensor, the DRL Module de-energizes the internal Head Relay and energizes the internal DRL Relay. Battery voltage is applied through the closed contacts of the DRL Relay to the DRL Diode. Due to the voltage drop across the DRL Diode, the LO Beam Headlamps are "ON" at a reduced intensity.

When the Park Brake Switch is closed (Park Brake set), CKT 33 is grounded. If the Ignition Switch is turned to "RUN" when CKT 33 is grounded, the DRL Module senses a voltage drop at the Park Brake Input and will not energize the Head Relay or the DRL Relay until the ground through CKT 33 is removed (Park Brake Switch open). Reapplying the Park Brake during the same Ignition cycle will not affect further DRL operation, during the same ignition cycle.