Daytime Running Lamp: Description and Operation

CIRCUIT OPERATION
The Daytime Running Lights (DRL) Module is designed to automatically operate certain 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 and the Lo Beam Headlights. The Diode Assembly reduces the voltage applied to the headlights, reducing the brilliance of the Headlights.

When the Photoresistor senses 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 as 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.

Photoresistor Input
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 the 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 car and keep the headlights off, as long as the Park Brake remains applied. This feature allows the operator to turn off the Headlights when the Ignition Switch is in RUN and is intended for use during service. When the Park Brake is released while the Ignition Switch is in RUN, the DRL Module will activate the Headlights.

This feature will function only when the Park Brake is applied before the Igntion 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 off the Lo Beam Headlights if it senses battery voltage at the Hi Beam On Output. This is to prevent the Lo Beam and Hi Beam Headlights from operating at the same time.