Principles of Operation
WARNING: This page is about a different car, the 2007 Lincoln Mark LT and 2007 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The daytime running lamps (DRL) operate by using the low beams at a reduced voltage. This is accomplished by inserting a DRL resistor in series with the low beam filaments. When the headlamp switch is turned to the HIGH or LOW beam position, the DRL relays are disabled and the low beam filaments receive 100% system voltage.