Daytime Running Lamp: Description and Operation

The Daytime Running Lights (DRL) Module is designed to automatically operate Exterior Lights depending on outside light conditions. The DRL Module operates in two modes. In the Day Mode, the LO Beam Headlights are lit at reduced brilliance. In the Night Mode, the LO Beam Headlights are lit at full brilliance and the Front Marker, Park and Tail Lights are lit.

When the DRL Module is in the Day Mode, the Day Mode contacts close, applying voltage to the Diode Assembly and the LO Beam Headlights. The Diode Assembly reduces the voltage applied to the Headlights, thus reducing the brilliance of the Headlights.

When the Photoresistor detects darkness, the DRL Module operates in the Night Mode. The Night Mode contacts close, applying voltage to the Headlights and other Exterior Lights through the same circuit path as when the Light Switch is in "HEAD."

If the Engine should stall with the DRL Module in the Night Mode, the DRL Module will turn off the Headlights and leave the Marker, Park and Tail Lights lit while the Engine is being cranked. The Light Switch operates as usual.

Photoresistor
The Photoresistor is a light sensitive variable resistor. Its resistance decreases as outside light intensity increases. The DRL Module measures the voltage drop across the Photoresistor 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 Module will not operate any Headlights or Exterior Lights. This allows the operator to start the vehicle and keep the Headlights off, as long as the Park Brake is applied. When the Park Brake is released with the Ignition Switch in "RUN," the DRL Module will activate the Headlights.

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 Headlights will not turn off.

"HI BEAM ON" Input
The DRL Module will turn the LO Beam Lamps "OFF" if it senses battery voltage at the "HI BEAM ON" input. This is to prevent the LO Beam and HI Beam Headlights from operating at the same time.