Part 2 of 3

HEADLAMP SWITCH
The headlamp switch is part of the left multi-function switch A knob on the end of the multi-function switch control stalk controls all of the exterior lighting switch functions. The exterior lighting switch is hard wired to the Body Control Module (BCM).

The exterior lighting switch cannot be adjusted or repaired and, if faulty or damaged, the entire left multi-function switch unit must be replaced. (Refer to ELECTRICAL/LAMPS/LIGHTING - EXTERIOR/TURN SIGNAL/HAZARD SWITCH - REMOVAL) for the service procedures. (Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/BODY CONTROL/CENTRAL TIMER MODUL - DESCRIPTION) for more information on this component.

The exterior lighting switch uses a hard wired 5 volt reference circuit from the BCM, resistor multiplexing and a hard wired switch output circuit to provide the BCM with a 0 - 5 volt signal that indicates the status of all of the exterior lighting switch settings. The BCM then uses control outputs to energize the headlamp and park lamp relays that activate the exterior lighting circuits.

The BCM monitors the exterior lighting switch status, then sends the proper switch status messages to other modules over the Programmable Communications Interface (PCI) data bus network. The exterior lighting switch status is also used by the BCM as an input for chime warning system operation.

Fig.22 Left (Lighting) Multi-Function Switch:

LEFT MULTI-FUNCTION SWITCH
The left multi-function switch, its mounting provisions, and its electrical connections are all concealed beneath the steering column shrouds, just below the steering wheel.

A single connector with eleven terminal pins is located on the back of the switch housing and connects the switch to the vehicle electrical system. The left multi-function switch supports the following exterior lighting functions:
- Auto Headlamps
- Front Fog Lamps
- Hazard Warning Control
- Headlamps
- Headlamp Beam Selection
- Headlamp Optical Horn
- Park Lamps
- Rear Fog Lamps
- Turn Signal Control

The left multi-function switch also supports the following interior lighting functions:
- Panel Lamps Dimming
- Interior Lamps Defeat
- Interior Lamps ON
- Parade Mode

The left multi-function switch cannot be adjusted or repaired. If any function of the switch is faulty, or if the switch is damaged, the entire switch unit must be replaced.

The left multi-function switch uses a combination of resistor multiplexed and conventionally switched outputs to control the many functions and features it provides using a minimal number of hard wired circuits. The switch is grounded to the chassis beneath the center floor console, just forward of the Airbag Control Module (ACM). Following are descriptions of the how the left multi-function switch operates to control the many exterior lighting functions and features it provides:
- Auto Headlamps - The automatic headlamps feature is provided by the Body Control Module (BCM), which monitors an input from a photodiode sensor located on the top of the instrument panel to detect ambient light levels whenever the ignition switch is in the ON position. Based upon the multiplexed input from the left multi-function switch and the input of the photodiode sensor, the BCM controls outputs to the park lamp and headlamp relays to illuminate or extinguish all exterior lighting.
- Front Fog Lamps - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that switched ground input, controls an output to the front fog lamp relay to illuminate or extinguish the front fog lamps.
- Hazard Warning Control - The hazard warning push button is pressed down to activate the hazard warning system, and pressed down again to turn the system off. The left multi-function switch provides a ground to the hazard warning sense input of the combination flasher to control activation of the hazard warning lamps.
- Headlamps - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, controls an output to the headlamp low or high beam relays to illuminate or extinguish the headlamps.
- Headlamp Beam Selection - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that switched ground input, controls an output to the headlamp low or high beam relays to activate the selected headlamp beam.
- Headlamp Optical Horn - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that switched ground input, controls an output to the headlamp high beam relay to activate the headlamp high beams.
- Park Lamps - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, controls an output to the park lamp relay to illuminate or extinguish the parking lamps.
- Rear Fog Lamps - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, controls an output to the rear fog lamp relay to illuminate or extinguish the rear fog lamps.
- Turn Signal Control - The left multi-function switch control stalk actuates the turn signal switch. The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, provides a variable voltage output to control the lighting of the turn signals.

Following are descriptions of the how the left multi-function switch operates to control the many interior lighting functions and features it provides:
- Panel Lamps Dimming - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, provides a variable voltage output through several panel lamps driver circuits to control the lighting of many incandescent panel lamps. The BCM also sends panel lamps dimming messages over the Programmable Communications Interface (PCI) data bus to other modules to control Display lighting levels in those modules.
- Interior Lamps Defeat - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, internally disables the function the BCM normally provides to control the illumination of the interior lamps.
- Interior Lamps ON - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, provides a control output to activate all of the interior lamp circuits.
- Parade Mode - The Body Control Module (BCM) monitors the left multi-function switch then, based upon that multiplexed input, provides a voltage output through several panel lamps driver circuits to control the lighting of many incandescent panel lamps. The BCM also sends panel lamps dimming messages over the Programmable Communications Interface (PCI) data bus to other modules on the bus to control lighting levels in those modules.

TAIL LAMP
The taillamp module contains a housing, lens, and three bulbs. A dual filament bulb is used for tail and stop functions. A single filament bulb is used for turn signal operations. A separate bulb is used for back-up illumination.

All exterior lighting function are controlled by the multifunction switch. Stop lamp functions are controlled by the stoplamp switch. The back-up lamps are controlled by the back-up lamp switch.

TURN SIGNAL CANCEL CAM
The turn signal cancel cam is concealed within the multi-function switch housing below the steering wheel and the clockspring mechanism. The turn signal cancel cam consists of a disc unit with two integral lobes. The upper lobe of the cam has an alignment hole that is used to align it with another hole in the back of the multi-function switch mounting housing. The upper surface of the turn signal cancel cam features three holes, two round and one oblong. These holes engage and key the cancel cam to three matching pins in the hub of the clockspring mechanism. The hub of the clockspring and the turn signal cancel cam rotate with the steering wheel. The centered clockspring housing is then secured to the multi-function switch mounting housing over the top of the turn signal cancel cam.

The turn signal cancel cam is serviced as a assembly with the multi-function switch housing. The turn signal cancel cam cannot be repaired and, if faulty or damaged, the multi-function switch mounting housing unit must be replaced. (Refer to ELECTRICAL/LAMPS/LIGHTING - EXTERIOR/LEFT MULTI- FUNCTION SWITCH - REMOVAL - MULTI- FUNCTION SWITCH MOUNTING HOUSING).

The turn signal cancel cam has two lobes. When the turn signals are activated by moving the left multi-function switch control stalk to a detent position, a turn signal cancel actuator is extended from the inside surface of the multi-function switch housing toward the center of the steering column and the turn signal cancel cam. When the steering wheel is rotated during a turning maneuver, one of the two turn signal cancel cam lobes will contact the turn signal cancel actuator. The cancel actuator latches against the cancel cam rotation in the direction opposite that which is signaled.