Headlamp: Description and Operation

Twilight Sentinel

The Twilight Sentinel System performs two functions. First, with the IGNITION SWITCH in "RUN," the system automatically turns the vehicle lamps on in darkness and out in daylight. Second, the system keeps vehicle exterior lamps on after the IGNITION SWITCH has been turned to "OFF." This function provides the driver and passengers with light after they have left the vehicle. The duration of lamp operation after the IGNITION SWITCH is turned "OFF" can be adjusted from a few seconds to 1 1/2 minutes using the SENTINEL CONTROL.

The SENTINEL AMPLIFIER receives voltage at all times through the ORN (240) and RED (2) wires. The SENTINEL AMPLIFIER also receives voltage through the PNK (3) wire whenever the IGNITION SWITCH is in "RUN," "BULB TEST," or "START." The SENTINEL AMPLIFIER is permanently grounded at G200.

As light intensity increases, the resistance of the SENTINEL PHOTOCELL decreases. Therefore, a lower voltage is sensed at the SENTINEL AMPLIFIER Photocell Signal during the day than at night. The Photocell Signal operates two switches in the SENTINEL AMPLIFIER. When the SENTINEL AMPLIFIER sees a low voltage signal at the SENTINEL PHOTOCELL terminal, the two switches open. When the two switches open, the voltage sources are removed from the exterior lamps. As light intensity decreases, the SENTINEL PHOTOCELL's resistance increases, voltage at the Photocell Signal increases, and the SENTINEL AMPLIFIER closes the two switches. When the two switches close, voltage is applied through the switches to the exterior lamps.

The Twilight Sentinel System also keeps exterior lamps on after the IGNITION SWITCH is turned to "OFF." A rheostat in the SENTINEL CONTROL enables the driver to vary the length of time that the SENTINEL AMPLIFIER keeps the lamps on. This time may be adjusted from just a few seconds up to approximately 1 1/2 minutes to provide driver and passengers security upon exiting the vehicle.

The entire system may be turned off and on with the SENTINEL CONTROL. With the system in "OFF," exterior lamp operation (using the LIGHT SWITCH) must be performed by the driver.

Daytime Running Lights

The Daytime Running Light System automatically turns the HI-BEAM HEADLAMPS on whenever the IGNITION SWITCH is in "RUN," the LIGHT SWITCH is "OFF," the GEAR SELECTOR SWITCH is moved out of "P" and the Sentinel Photocell indicates daytime light conditions. When the SENTINEL AMPLIFIER receives these inputs, it pulses voltage to the vehicle's HI-BEAM HEADLAMPS. This pulsing illuminates the HI-BEAM HEADLAMPS at a slightly lower intensity than they sustain during normal HI-BEAM HEADLAMP operation. A different SENTINEL AMPLIFIER module is used on vehicles equipped with Daytime Running Lights than on vehicles equipped with Twilight Sentinel only.