Daytime Running Lamp: Description and 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. In the Day Mode, the LOW Beam Headlamps are lit at reduced brilliance. In the Night Mode, the LOW Beam Headlamps are lit at full brilliance and the Front Marker, Park and Tail Lamps are lit. When the DRL Control Module is in the Day Mode, the Day Mode contacts close, applying voltage to the DRL Diode and the LOW Beam Headlamps. The DRL Diode reduces the voltage applied to the Headlamps, thus reducing the brilliance of the Headlamps.

When the Ambient Light Sensor senses darkness, the DRL Control Module operates in the Night Mode. The Night Mode contacts close, applying voltage to the Headlamps and other Exterior lights through the same circuit path as when the Headlamp Switch is in "HEAD." 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 Marker, Park and Tail Lamps lit while the Engine is being cranked. The Headlamp Switch operates as usual.

Ambient Light Sensor Input
The 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 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.