Headlamp: Description and Operation

The headlamps are controlled either by the Daytime Running Lamps (DRL) Control Module or by the Light Switch/Dimmer Switch. Once the Light Switch has been turned to "HEAD", the Dimmer Switch will control the headlamps. With the Dimmer Switch in LO, ground is provided to the low beam filaments through the DRL Control Module, Junction Block, Dimmer Switch, back through the Junction Block, through the closed contacts of Light 2 Relay to G201. Since voltage is applied to the headlamps at all times through the HI LH Fuse and the HI RH Fuse, the low beam filaments will light.

With the Dimmer Switch in "HI", the high beam filaments in the headlamps are grounded through the Junction Block, Dimmer Switch, back through the Junction Block, through the closed contacts of Light 2 Relay to G201. Since voltage is applied to the headlamps at all times through the HI LH Fuse and the HI RH Fuse, the high beam filaments will light. The ground to the High Beam Indicator is provided in the same manner as the high beam filaments. Since voltage is applied to the High Beam Indicator at all times through the HI LH Fuse, the indicator will light.

With the Dimmer Switch in "PASS", the high beam filaments in the headlamps are grounded through the Junction Block and Dimmer Switch to G201. Since voltage is applied to the headlamps at all times through the HI LH Fuse and the HI RH Fuse, the high beam filaments will light. The ground to the High Beam Indicator is provided in the same manner as the high beam filaments. Since voltage is applied to the High Beam Indicator at all times through the HI LH Fuse, the indicator will light.

With the Ignition Switch m ON" or "START", voltage is applied to the DRL Control Module through the 16 Fuse. The DRL Control Module is permanently grounded to G201. A number of conditions must be met before the Daytime Running Lamps system will work properly: the parking brake must be disengaged, the DRL Control Module must not receive a ground signal from the Generator (a ground signal from the generator indicates that the generator is not charging the battery) and the Light Switch is either in "OFF" or in PARK position. When the parking brake is engaged, the Parking Brake Switch turn loses, providing a ground to the DRL Control Module, disabling DRL operation. When the Generator is not running, a switch in the Generator closes, providing a ground to the DRL Control Module, disabling DRL operation. When the Light Switch is in the HEAD position, a path to G201 is provided to the coil of Light 2 Relay. Since power is provided to the coil of Light 2 Relay at all times through either the HI LH Fuse or the HI RH Fuse and through Diode No.3, the contacts on the relay close, providing a ground path from the DRL Control Module to G201, disabling DRL operation.

Once all of the listed conditions for DRL operation are met, the DRL Control Module will provide a ground for the low beam filaments in the headlamps through the Daytime Running Lamps Resistor to G102. Since voltage is applied to the headlamps at all times through the HI LH Fuse and the HI RH Fuse, the low beam filaments will light at 80% intensity.

The DRL Control Module will also provide a ground to the Daytime Running Lamps Indicator when the DRL operation conditions are met. Since voltage is applied to the Daytime Running Lamps Indicator through the 16 Fuse, it will light.