Lamps/Lighting - Exterior

The exterior lighting system for this model includes the following exterior lamp units:
- Center High Mounted Stop Lamp (3) - A standard equipment Center High Mounted Stop Lamp (CHMSL) is centered on the cab roof header panel just above the glass opening at the rear of the cab. This CHMSL also incorporates two integral cargo lamps, one located at each outboard side of the CHMSL.
- Front Fog Lamps (2) - Vehicles equipped with this option have a fog lamp unit mounted near each outboard end of the front bumper support, behind the lower portion of the front fascia.
- Front Lamp Units (1) - A standard equipment front lamp unit is mounted to the front of each front fender panel on either side of the grille opening.
- License Plate Lamp (4) - A standard equipment rear license plate lamp unit is mounted to each outboard vertical surface of the license plate tub formation in the center of the rear bumper.
- Rear Lamp Units (5) - A standard equipment rear lamp unit is mounted to the rear of each quarter panel on either side of the tailgate opening.

These exterior lighting lamp units and their controls are combined to provide the following exterior lighting features:
- Automatic Headlamps - Vehicles with the automatic headlamps option are equipped with a unique headlamp switch that includes an automatic position and a sun load sensor located on the top of the instrument panel to sense ambient light levels. When the Auto position of the headlamp switch is selected, the headlamps are turned On automatically when ambient light levels are low.
- Backup Lamps - The backup (or reverse) lamps include a bulb, reflector and lens that are integral to each rear lamp unit.
- Brake Lamps - The brake (or stop) lamps include a bulb, reflector and lens that are integral to each rear lamp unit, and the CHMSL bulb and lens.
- Daytime Running Lamps - Vehicles manufactured for sale in Canada illuminate the high beam filament of the headlamp bulb in each front lamp unit to serve as the Daytime Running Lamps (DRL). Fleet vehicles manufactured for sale in the United States illuminate the low beam filament of the headlamp bulb in each front lamp unit to serve as the DRL.
- Exterior Lamp Fail-Safe Operation - The EMIC provides a fail-safe feature which will automatically turn on the low beam headlamps and all park lamps when the ignition switch is in the On position and there is no detected input from the headlamp switch.
- Exterior Lamp Load Shedding - The Front Control Module (FCM) provides a battery saver feature which will automatically turn off all exterior lamps that remain on with the ignition switch in the Lock position after a timed interval of about eight minutes.
- Front Fog Lamps - The optional front fog lamps include the bulb, reflector and lens of each adjustable front fog lamp unit.
- Hazard Warning Lamps - The hazard warning lamps include the right and left turn signal bulbs, reflectors and lenses of each front and rear lamp unit.
- Headlamps - The headlamps include a single, dual filament halogen bulb, an adjustable reflector and a clear lens integral to each front lamp unit.
- Optical Horn - Also known as flash-to-pass, the beam selection function of the multi-function switch control stalk has a momentary intermediate position that allows the headlamp high beams to be flashed momentarily, without changing the headlamp beam selection.
- Park Lamps - The park lamps include the park and side marker bulbs, reflectors and lenses integral to each front and rear lamp unit as well as the bulbs and lenses of the rear license plate lamps.
- Turn Signal Lamps - The turn signal lamps include the turn signal bulbs, reflectors and lenses that are integral to the right and left front and rear lamp units.

Other components of the exterior lighting system for this model include:
- Backup Lamp Switch - A plunger-type backup lamp switch is installed through the transmission housing of vehicles equipped with a manual transmission and is actuated by the shifter mechanism within the transmission when Reverse gear is selected. Depending upon the transmission model, either a stand-alone Transmission Range Sensor (TRS), or a TRS that is integral to the solenoid pack on the valve body performs the backup lamp switch function on vehicles with an automatic transmission.
- Brake Lamp Switch - A plunger-type brake lamp switch is located on the steering column support bracket under the instrument panel and is actuated by the brake pedal arm when the brake pedal is depressed.
- Front Control Module - The Front Control Module (FCM) is integral to the Integrated Power Module (IPM). The FCM/IPM is located in the engine compartment, near the battery and the Power Distribution Center (PDC).
- Front Fog Lamp Relay - Vehicles equipped with optional front fog lamps have a front fog lamp relay located in the Power Distribution Center (PDC).
- Headlamp Switch - A headlamp switch is located on the left side of the instrument panel, below and outboard of the steering column. The headlamp switch includes a rotary knob that is rotated to turn the park lamps and headlamps On or Off, and a push button switch for selecting the cargo lamps. The rotary knob is pushed inward for selecting the optional front fog lamps on vehicles so equipped. The headlamp switch also features a vertical thumbwheel for selecting the panel lamps dimming level, a Parade mode to illuminate all Vacuum Fluorescent Display (VFD) units at full brightness for visibility when driving in daylight with the exterior lighting turned On, and for interior lighting control.
- Instrument Cluster - The ElectroMechanical Instrument Cluster (EMIC) is also known as the Cab Control Node (CCN) in this vehicle. The EMIC/CCN is located in the instrument panel above the steering column opening, directly in front of the driver.
- Multi-Function Switch - The multi-function switch is located on the steering column, just below the steering wheel. A control stalk that extends from the left side of the switch is used to select the turn signal lamps (right or left) and to select the headlamp beam (low, high or optical horn). A push button that extends from the top of the switch is used to select the hazard warning lamps.
- Park Brake Switch - A park brake switch is located on the park brake lever mechanism on the cowl side inner panel below the instrument panel, to the left of the steering column.
- Park Lamp Relay - A park lamp relay is located in the Power Distribution Center (PDC) of all vehicles.
- Trailer Tow Relays - Vehicles equipped with a factory-installed trailer towing package have two trailer tow relays installed in the Power Distribution Center (PDC) in the engine compartment, one for the trailer right turn and brake lamps and the other for the trailer left turn and brake lamps.
- Trailer Tow Wiring - Vehicles equipped with a factory-installed trailer towing package have a trailer tow wire harness and both a 4-way and a heavy duty 7-way trailer tow connector installed on a bracket on the trailer hitch receiver. This package also includes an electric trailer brake wiring provision that terminates at a connector located on top of the large body harness connection under the instrument panel to the left of the brake pedal, as well as an electric trailer brake pigtail harness and an instruction card that are stored in the glove box when the vehicle is shipped from the factory.

Hard wired circuitry connects the exterior lighting system components to the electrical system of the vehicle. These hard wired circuits are integral to several wire harnesses, which are routed throughout the vehicle and retained by many different methods. These circuits may be connected to each other, to the vehicle electrical system and to the exterior lighting components through the use of a combination of soldered splices, splice block connectors, and many different types of wire harness terminal connectors and insulators.The wiring information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices and grounds.

Following are paragraphs that briefly describe the operation of each of the major exterior lighting systems. The hard wired circuits and components of the exterior lighting systems may be diagnosed and tested using conventional diagnostic tools and procedures.

However, conventional diagnostic methods may not prove conclusive in the diagnosis of the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Control Node/CCN), the Front Control Module (FCM) (also known as the Integrated Power Module/IPM), the Powertrain Control Module (PCM) or the Controller Area Network (CAN) data bus. The most reliable, efficient, and accurate means to diagnose the EMIC, the FCM, the PCM, the CAN data bus or the electronic bus message inputs and outputs related to the various exterior lighting systems requires the use of a diagnostic scan tool.

BACKUP LAMP
The backup (or reverse) lamps have a path to ground at all times through a takeout and eyelet terminal of the left headlamp and dash wire harness that is secured by a ground screw to the left inboard side of the hydroform within the engine compartment. On vehicles with a manual transmission, the backup lamp switch provides an input to the Front Control Module (FCM) and the FCM provides battery voltage to the backup lamps on the backup lamp feed circuit whenever the ignition switch is in the On position and the Reverse position is selected with the transmission shift linkage.

On vehicles with an automatic transmission, the PCM continually monitors a hard wired multiplex input from the Transmission Range Sensor (TRS), then sends the proper transmission gear selector status messages to other electronic modules over the CAN data bus. When the FCM receives an electronic message indicating the status of the transmission gear selector is Reverse, it provides a battery voltage output to the backup lamps on the backup lamp feed circuit.

BRAKE LAMP
The brake (or stop) lamps each have a path to ground at all times through a takeout and eyelet terminal of the left headlamp and dash wire harness that is secured by a ground screw to the left inner fender support within the engine compartment. The Center High Mounted Stop Lamp (CHMSL) has a path to ground at all times through a takeout and eyelet terminal of the body wire harness that is secured by a nut to a ground stud to the left sill at the base of the cowl side inner panel. The brake lamps and CHMSL receive battery voltage on the brake lamp switch feed circuit when the brake lamp switch is closed by the brake pedal arm. The CHMSL and brake lamps are connected to a hard wired output from the brake lamp switch. The brake lamp function of the trailer tow stop/turn relays is controlled by an output from the Front Control Module (FCM) based upon a hard wired input from the brake lamp switch.

DAYTIME RUNNING LAMPS
Vehicles manufactured for sale in Canada illuminate the high beam filament of both headlamp bulbs at a reduced intensity when the engine is running and the exterior lamps are turned off. Fleet vehicles manufactured for sale in the United States illuminate the low beam filament of both headlamp bulbs at a reduced intensity when the engine is running, the parking brakes are released and the exterior lamps are turned off. The FCM must be programmed appropriately for this feature to be enabled. Once enabled, anytime the FCM receives electronic messages over the CAN data bus from the PCM indicating the engine is running and from the EMIC indicating the status of the headlamp switch exterior lighting input is Off and that the parking brakes are released, the FCM provides a pulse width modulated voltage output to the proper headlamp bulb filaments through the right and left beam feed circuits to produce illumination at a reduced intensity.

FRONT FOG LAMPS
Vehicles equipped with optional front fog lamps include a front fog lamp relay installed in the PDC, and a front fog lamp switch integral to the headlamp switch on the instrument panel. The front fog lamps have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the right (right fog lamp) and left (left fog lamp) inboard sides of the hydroform within the engine compartment. The EMIC monitors a hard wired multiplex input from the headlamp switch to determine whether the fog lamps are selected, then sends electronic fog lamp switch status messages to the FCM over the CAN data bus.

When the FCM receives a fog lamp status message it then controls front fog lamp operation by energizing or deenergizing the front fog lamp relay control coil. The FCM also sends the appropriate electronic message back to the EMIC to illuminate or extinguish the front fog lamp indicator. When the front fog lamp relay is energized, it provides battery voltage from a fused B(+) fuse in the PDC to the fog lamps through the fog lamp relay output circuit. The FCM will automatically de-energize the front fog lamps relay any time the headlamp high beams are selected. The FCM also provides a battery saver (load shedding) feature for the front fog lamps, which will turn these lamps off if they are left on for more than about eight minutes with the ignition switch in the Lock position. Each front fog lamp includes an integral adjustment screw to be used for static aiming of the fog lamp beams.

HAZARD WARNING LAMPS
The hazard warning system includes the EMIC, the FCM and the multi-function switch on the steering column. The EMIC monitors a hard wired multiplex input from the multi-function switch to determine the status of the hazard warning switch, then sends the appropriate electronic hazard switch status messages to the FCM over the CAN data bus. The FCM responds to these messages by controlling a battery voltage output and the flash rate for each of the right and left turn signal lamps. The FCM also sends the appropriate electronic messages back to the EMIC to control the illumination and flash rate of the right and left turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the EMIC electronic circuit board that emulates the sound emitted by a conventional hazard warning flasher.

HEADLAMPS
The headlamp system includes the EMIC, the FCM, the multi-function switch on the steering column and the headlamp switch on the instrument panel. The headlamp bulbs have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the right (right headlamp bulb) and left (left headlamp bulb) inboard sides of the hydroform within the engine compartment.

The EMIC monitors a hard wired multiplex input to determine the status of the headlamp switch, and a hard wired multiplex input from the multi-function switch to determine whether the high or low beams are selected. The EMIC then sends the appropriate electronic headlamp switch and headlamp beam select switch status messages to the FCM over the CAN data bus. The FCM responds to these messages by providing a pulse width modulated voltage output to the proper headlamp bulb through the right and left low and high beam feed circuits to illuminate the selected headlamp filaments.

The FCM also remembers which beams (low or high) were selected when the headlamps were last turned Off, and energizes those beams again the next time the headlamps are turned On. The FCM provides a battery saver (load shedding) feature for the headlamps, which will turn these lamps off if they are left on for more than about eight minutes with the ignition switch in the Lock position. The EMIC provides a fail-safe feature for the headlamps, which will send an electronic message to the FCM to turn the low beam headlamps On automatically if it detects no input from the headlamp switch. Each headlamp includes an integral reflector adjustment screw to be used for static aiming of the headlamps.

PARK LAMPS
The park lamps system includes the EMIC, the FCM, a park lamp relay installed in the PDC, and the headlamp switch on the instrument panel. The front park lamp and side marker lamp bulbs each have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the right (right park lamp and side marker lamp bulbs) and left (left park lamp and side marker lamp bulbs) inboard sides of the hydroform within the engine compartment. The rear park lamp, side marker lamp and license plate lamp bulbs have a path to ground at all times through a takeout and eyelet terminal of the left headlamp and dash wire harness that is secured by a ground screw to the left inboard side of the hydroform within the engine compartment.

The EMIC monitors a hard wired multiplex input from the headlamp switch, then sends the appropriate electronic headlamp switch status messages to the FCM over the CAN data bus. The FCM responds to these messages by energizing or de-energizing the park lamp relay. When the park lamp relay is energized, it provides battery voltage from a fuse in the PDC through a park lamp relay output circuit to the appropriate lamp bulbs. The FCM provides a battery saver (load shedding) feature for the park lamps, which will turn these lamps off if they are left on for more than about eight minutes with the ignition switch in the Lock position. The EMIC provides a fail-safe feature for the park lamps, which will send an electronic message to the FCM to turn these lamps on automatically if it detects no input from the headlamp switch.

TRAILER TOW WIRING
In addition to the trailer tow wiring provisions, vehicles equipped with an optional trailer tow package include right and left trailer tow stop/turn relays installed in the PDC. When the FCM receives the appropriate inputs for normal turn signal, hazard warning or brake lamp operation, it responds by also energizing or de-energizing these trailer tow relays. When a trailer tow relay is energized, it provides battery voltage from a fused B(+) fuse to the trailer lamps through the trailer tow wiring to synchronize the illumination and flash rate of the trailer brake and turn signal lamps with those of the tow vehicle.

TURN SIGNAL LAMPS
The turn signal lamps system includes the EMIC, the FCM and the multi-function switch on the steering column. The front turn signal lamp bulbs each have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the right (right front turn signal lamp bulb) and left (left front turn signal lamp bulb) inboard sides of the hydroform within the engine compartment. The rear turn signal lamp bulbs have a path to ground at all times through a takeout and eyelet terminal of the left headlamp and dash wire harness that is secured by a ground screw to the left inboard side of the hydroform within the engine compartment.

The EMIC monitors a hard wired multiplex input from the multi-function switch to determine the status of the turn signal switch, then sends the appropriate electronic turn signal switch status messages to the FCM over the CAN data bus. The FCM responds to these messages by controlling a battery voltage output and the flash rate for either the right or left turn signal lamps. The FCM also sends the appropriate electronic messages back to the EMIC to control the illumination and flash rate of the right or left turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the EMIC electronic circuit board that emulates the sound emitted by a conventional turn signal flasher.

The EMIC also provides a "turn signal on warning" that will generate repetitive chimes to indicate that a turn signal has been active continuously for 1.6 kilometers (1 mile) with the vehicle speed greater than 22 kilometers-per-hour (15 miles-per hour). Vehicles built for markets other than the United States and Canada have a revised distance threshold of 4 kilometers for this feature. The chime will continue until the turn signal input becomes inactive or until the vehicle speed message indicates that the speed is less than 22 kilometers-per-hour (15 miles-per-hour, whichever occurs first.