Daytime Running Lamp: Description and Operation

CIRCUIT OPERATION
With the LIGHT SWITCH in the OFF or PARK position and the engine running, Daytime Running Lights (DRL) operation is achieved by applying system voltage from the GENERATOR, through the closed contacts of the Restart Relay, to the coils of DRL Relay-1, DRL Relay-3 and the DRL Cut Relay. The coils of DRL Relays 1 and 3 are provided a ground at G103 through the closed contacts of both the DRL Cut Relay (de-energized) and DRL Relay-2 (also de-energized).

With both voltage and ground provided to the coil of Daytime Running the relay is energize, the terminal 2-6 contacts close, and system voltage from FL-2 is applied through Fuses E-7 and E-8 to the HEADLAMPS.

With both voltage and ground provided to the coil of DRL Relay-1, the relay is energized, and the contacts are pulled to provide only the LOW-BEAM HEADLAMPS a ground at G103 through the DRL RESISTOR. Because of the DRL RESISTOR in the ground circuit, the LOW-BEAM HEADLAMPS operate at approximately 85 percent brilliance.

Whenever the parking brake is engaged, the coil of the DRL Cut Relay is provided a ground at the PARKING BRAKE SWITCH. With both voltage and ground provided, the DRL Cut Relay is energized, the contacts are pulled open, and the ground circuit for both DRL Relays 1 and 3 is interrupted. In this manner, DRL operation is terminated whenever the parking brake is engaged.

As long as the engine is running and the LIGHT SWITCH is not in the HEAD position, DRL Relay-3 will remain energized. With this relay energized, its terminal 4-5 contacts are open and high beam operation is disabled by interrupting the only possible ground circuit for the HIGH-BEAM HEADLAMPS.

With the LIGHT SWITCH in the HEAD position, the coil of DRL Relay-2 is provided a ground through the LIGHT SWITCH to G201. Because the coil is provided system voltage at all times through FL-2, DRL Relay-2 energizes, its terminal 1-2 contacts close, its terminal 4-5 contacts open, and voltage is applied to the coil of the Lighting Relay. Because the coil of the Lighting Relay is permanently grounded at G102, the relay energizes as soon as voltage is applied. When this relay energizes, its contacts close and voltage is applied through Fuses E-7 and E8 to the HEADLAMPS.

Because the 4-5 contacts of DRL Relay-2 are now open, the ground circuit for the coils of DRL Relay-1 and DRL Relay-3 is interrupted. This action causes the contacts of DRL Relay-1 to swing to their de-energized position. This position provides an unresisted ground through the LO contacts of the Dimmer/Passing Switch to G201 - causing the HEADLAMPS to light at full brilliance.

Whenever the Dimmer/Passing Switch is pulled back and released, the LO contacts open and the HI contacts close. Repeated action of the switch toggles the contact positions back and forth between LO and HI. With the HI contacts closed, the HIGH-BEAM HEADLAMPS are provided a ground at G201 through the closed contacts of DRL Relay-3 and the HI contacts of the Dimmer/Passing Switch.

When the Dimmer/Passing Switch is pulled back and held, the Flash-to-Pass (FTP) contacts are pulled closed. The FTP contacts ground the coil of DRL Relay-2 at G201. Because the coil receives voltage at all times from FL-2. DLR Relay-2 is energized as soon as the ground is provided. With the relay energized, its terminal 1-2 contacts close and voltage is applied to the coil of the Lighting Relay. Because the coil of Lighting Relay is permanently grounded at G102, the relay energizes as soon as voltage is applied. When energized, its terminal 2-4 contacts close and voltage is applied through Fuses E-7 and E-8 to the HEADLAMPS.

Because a ground is provided at G201 through the FTP contacts in the Dimmer/Passing Switch, the HIGH-BEAM HEADLAMPS operate as soon as voltage is applied. Further, because pulling the Dimmer/Passing Switch always toggles the LO/HI contacts, one of two actions will occur. If the Dimmer/Passing Switch was in the LO position when it was pulled back, the LO contacts will open, the HI contacts will close, and only the HIGH BEAM HEADLAMPS will operate when the FTP contacts are closed. If, however, the Dimmer/Passing Switch was in the HI position when pulled back, the HI contacts will open, the LO contacts will close, and because all of the HEADLAMPS are not provided both voltage and ground, they will all operate.