Headlamp: Description and Operation

The headlamps may be turned on in three different ways:
^ When the headlamp switch is placed in the ON position, for normal operation.
^ When the headlamp switch is placed in the OFF position, and the twilight delay switch is moved out of the OFF position for Automatic Lamp Control (ALC).
^ When the headlamp switch is placed in the OFF position, the twilight delay switch is moved out of the OFF position, and the windshield wipers are ON in daylight conditions, after a six second delay.

During ALC control the headlamps will be in Day Time Running Lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions. When all exterior lighting controls are inactive and nighttime conditions are sensed, a HEADLAMPS SUGGESTED message will appear on the Driver Information Center (DIC), after the IPC receives a class 2 message from the DIM. The message will also appear if the wiper activated headlamps feature is off due to the twilight sentinel being off, but the windshield wipers are on. The Dash Integration Module (DIM) provides battery positive voltage to the signal circuits of the headlamp switch. The signal circuits include the Head Lamp Switch input, and the Flash To Pass Switch.

With the headlamp switch in the ON position, the headlamps on signal circuit is grounded through the headlamp switch to G200. In response to this input, the DIM provides ground to the HDLP LO BM relay control circuit. The IPC illuminates the LIGHTS ON indicator when the DIM detects that the headlamps are requested. When the headlamp dimmer switch lever is pushed away from the driver to the HIGH BEAM position, the HDLP HI BM relay has ground through the headlamp dimmer switch. This Illuminates the high beam headlamps in addition to the low beams. The IPC illuminates the high beam indicator when the DIM detects that the high beam headlamps are requested. The DIM supplies battery positive voltage to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to both relay switch circuits. When the low beam relay coil is energized, current flows through the HDLOBML fuse and the HDLOBMR fuse to the low beam headlamps. The headlamps have ground at G401. When the HDLP HI BM relay coil is energized, current flows through the HDHIBML fuse and the HDHIBMR fuse to the high beam headlamps. The high beam circuit is divided into a left and right side circuit. The current flow of the left high beam is from the fuse to the left high beam lamp. From the lamp, the current flows to the normally-closed contact of the Daytime Running Lamp (DRL) relay to G104. The current flow of the right high beam is from the fuse to the right high beam headlamp. From the lamp, the current flow is to ground at G401. When the headlamp dimmer switch lever is pulled toward the driver, the Flash-To-Pass switch closes. This grounds the DIM Flash-To-Pass input. In response to this input, the DIM energizes the high beam relay. Both high beams remain on until the driver releases the switch handle. If the low beam headlamps were on during Flash-To-Pass operation, the low beams remain on.