Principles of Operation

WARNING: This page is about a different car, the 2006 Ford F550 Super Duty, 2006 Ford F450 Super Duty, and 2006 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

The DRL operate by using the low beams at a voltage approximately 80% of system voltage. This is accomplished by a resistor in series with the low beam filaments.

When the parking brake is applied, the DRL relay 1 is energized and interrupts the voltage to the remaining DRL relays. This disables the DRL function.

When the headlamp switch is placed in the headlamps ON position, the DRL relay 2 is energized and interrupts the voltage to the DRL relay 3. This disables the DRL function and the low beam filaments receive 100% system voltage.

The DRL relay 3 determines the voltage source to the headlamps. When the DRL relay 3 is energized, the headlamps receive 80% voltage from the DRL resistor. When the DRL relay 3 is not energized, the headlamps receive 100% voltage from the headlamp switch.