Lighting Systems: Other Chevrolet Silverado 3500

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Backup Lamps Always On

Backup Lamps Always On

Backup Lamps Inoperative

Backup Lamps Inoperative

Cargo Lamp Always On

Cargo Lamp Always On

Cargo Lamp Inoperative

Cargo Lamp Inoperative

Clearance Lamps Inoperative

Clearance Lamps Inoperative

Courtesy Lamps Always On

Courtesy Lamps Always On

Courtesy Lamps Inoperative

Courtesy Lamps Inoperative

Daytime Running Lamps (DRL) Always On

Daytime Running Lamps (DRL) Always On

Daytime Running Lamps (DRL) Inoperative (Domestic)

Daytime Running Lamps (DRL) Inoperative (Domestic)

Exterior Courtesy Lamp(s) Always On

Exterior Courtesy Lamp(s) Always On

Exterior Courtesy Lamp(s) Inoperative

Exterior Courtesy Lamp(s) Inoperative

Fog Lamp Indicator Inoperative

Fog Lamp Indicator Inoperative

Fog Lamp Indicator Inoperative - Rear

Fog Lamp Indicator Inoperative - Rear

Fog Lamps Always On

Fog Lamps Always On

Fog Lamps Inoperative

Fog Lamps Inoperative

Fog Lamps Always On - Rear

Fog Lamps Always On - Rear

Fog Lamps Inoperative - Rear

Fog Lamps Inoperative - Rear

Hazard Lamps Always On

Hazard Lamps Always On

Hazard Lamps Inoperative

Hazard Lamps Inoperative

Headlamps Always On - Low or High Beam

Headlamps Always On - Low or High Beam

Headlamps Inoperative - High Beams

Headlamps Inoperative - High Beams

Headlamps Inoperative - Low Beams

Headlamps Inoperative - Low Beams

Headlamps Inoperative - Low and High Beams

Headlamps Inoperative - Low and High Beams

Headlamps Inoperative - Flash to Pass

Headlamps Inoperative - Flash to Pass

Headlight Leveling Inoperative

Headlight Leveling Inoperative

High Beam Indicator Always On

High Beam Indicator Always On

High Beam Indicator Inoperative

High Beam Indicator Inoperative

Interior Backlighting Does Not Dim

Interior Backlighting Does Not Dim

Interior Backlighting Inoperative

Interior Backlighting Inoperative

Park, License, and Tail Lamps Always On

Park, License, and Tail Lamps Always On

Park, License, and Tail Lamps Inoperative

Park, License, and Tail Lamps Inoperative

Reading Lamp(s) Inoperative

Reading Lamp(s) Inoperative

Roof Beacon Lamp Always On

Roof Beacon Lamp Always On

Roof Beacon Lamp Inoperative

Roof Beacon Lamp Inoperative

Stop Lamps Always On

Stop Lamps Always On

Stop Lamps Inoperative

Stop Lamps Inoperative

Turn Signal Lamps and/or Indicators Always On or Flashing

Turn Signal Lamps and/or Indicators Always On or Flashing

Turn Signal Lamps and/or Indicators Inoperative

Turn Signal Lamps and/or Indicators Inoperative

Vanity Mirror Lamp(s) Inoperative

Vanity Mirror Lamp(s) Inoperative

Headlamp Aiming

Headlamp aiming is done with the vehicle's low beam lamps. The high beam lamps will be correctly aimed if the low beam lamps are aimed properly. If the high beam needs adjustment, follow the screen method using the high beam bulb as the reference for measurements.

Screen Method for Headlamp Aiming (Visual Aim)

Headlamp aim should be checked

1. When a new headlamp capsule is installed
2. If service or repairs to the front end area have (or may have) disturbed the headlamps or their mounting

Scheme 20

1. The area will consist of a level surface large enough to allow for a vehicle and an additional 7.62 m (25 feet) measured from face of lamps to the front of the aiming screen.
2. The screen will be 1.52 m (5 ft) high x 3.66 m (12 ft) wide with a matte white surface well shaded from extraneous light, and properly adjusted to the floor on which the vehicle stands. Provisions may be made for moving the screen so it can be aligned parallel with the vehicle.
3. The screen shall be provided with a fixed vertical centerline, two laterally adjustable vertical tapes, and one vertically adjustable horizontal tape.
4. If a regular commercial aiming screen is not available, the screen may consist of a vertical wall having a clear uninterrupted area approximately 1.83 m (6 ft) high and 3.66 m (12 ft) wide. The surface should be finished with a washable non-gloss white paint.
5. After the aiming screen has been set up in its permanent location, it is necessary to paint a reference line on the floor directly under the lens of the lamps to indicate the proper location of the headlamps when they are being aimed: Distance between headlamps (1) Center line of screen (2) Adjustable vertical pointer (3) Adjustable horizontal tape (4) Diagram of light screen (5) Vertical center line ahead of right headlamp pointer position (6) 7.62 m (25 ft) (7) Car axis (8) Adjustable vertical pointer Horizontal center line of lamps Vertical center line ahead of left headlamp

Prior to aiming the headlamps, the following steps must be taken

1. Remove any snow, ice or mud from the vehicle.
2. The vehicle must have a full tank of gas.
3. Stop all other work on the vehicle.
4. If any service has been performed on the vehicle, make sure that all of the components are back in their original place.
5. The vehicle must be on a level surface.
6. The vehicle left tires must be aligned with the reference line extending from the screen with the headlamps aligned with the reference line.
7. Do not load any cargo in the vehicle.
8. The vehicle must contain one person or 72.56 kg (160 lb) on the driver's seat.
9. Inflate the tires to the proper pressure.
10. Simulate the vehicle loads if the intended use of the vehicle is for hauling heavy loads or towing a trailer.
11. Rock the vehicle in order to stabilize the suspension.
12. Turn on the headlamps to low beam and observe the left and the top edges of the high intensity zone on the screen. The edges of the high intensity zone should fall within the specifications.

Headlamp Aiming Procedure

1. Open the hood.
2. Measure from the floor to the center of the headlamp bulb. (Some headlamps have an aim dot marked on the headlamp lens).
3. At the screen, measure from the floor and place the horizontal tape at the measured distance.
4. Measure from the reference line on the floor to the left headlamp bulb centerline.
5. At the screen, measure from the reference line and place the vertical tape at the measured distance.
6. Measure from the reference line on the floor to the right headlamp bulb centerline.
7. At the screen, measure from the reference line and place the vertical tape at the measured distance.
8. Turn on the low beam headlamps and block the light from projecting onto the screen from the passenger side headlamp.
9. Adjust the vertical aim of the headlamps to the specifications required by the state and the local authorities, or as shown in step number 8.
10. Rotate the headlamp adjuster to change the vertical aim of the headlamp.
11. Repeat the aiming procedure for the passenger side headlamp while blocking the light from projecting onto the screen from the driver side headlamp.
12. Close the hood.
13. This illustration represents the visual optics left (VOL) pattern.
14. This illustration represents the visual optics right (VOR) pattern.
15. This illustration represents all headlamps, except the VOL and VOR.
16. This illustration represents the high beam pattern for all headlamps, including VOL and VOR.

Scheme 21

Fog Lamp Replacement - Front

Fog Lamp Aiming Procedure

The front fog lamps must be aimed for proper illumination of the road. The front fog lamp aim should be checked when a new front fog lamp assembly is installed, or if service or repairs in the front end area may have disturbed the front fog lamp mounting.

Preparation Procedure

1. Completely assemble all of the components on the vehicle.
2. Park the vehicle on a level surface.
3. Stop all unnecessary operations or work on the vehicle that affect the vehicle trim.
4. Close the doors and ensure that the vehicle has no load other than the driver.
5. Stabilize the suspension by rocking the vehicle sideways.
6. Ensure that the fuel level is 1/2 full.
7. Ensure that the tires are inflated to the proper pressure.
8. Ensure that the driver or a similar weight, approximately 75 kg (165 lb), is in the vehicle driver seat.

Aiming Procedure

1. Park the vehicle on a level surface 7.6 m (25 ft) away from a wall or other flat surface.
2. Measure the distance from the floor to the center of the fog lamp (5).
3. Using this measurement, mark the horizontal centerline of the fog lamp (1) on the flat surface directly in front of the vehicle.
4. Turn ON the fog lamps.
5. Reach under the rear lower edge of the front fascia in order to access the fog lamp vertical adjustment screw on the rear of the fog lamp.
6. Adjust the fog lamp so that the top edge of the fog lamp beam pattern is 100 mm (4 in) below the horizontal centerline.
7. Turn OFF the fog lamps.

Exterior Lamps

The exterior lighting system consist of the following lamps

1. The headlamps
2. The daytime running lamps (DRL)
3. The fog lamps
4. The park, tail and marker lamps
5. The exterior courtesy lamps
6. The turn signal/hazard lamps
7. The stop lamps
8. The backup lamps
9. The cargo lamps
10. The clearance lamps
11. The roof beacon lamp

Headlamps

The headlamps may be turned on in 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC the headlamps will be in day time running lamp (DRL) operation in daylight conditions, or headlamp operation in low light conditions.

Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch headlamp on signal circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.

If the headlamp switch is left in the ON position, the inadvertent power control feature will turn off the headlamps approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlamp switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlamps will remain ON until turned OFF or the battery runs dead.

High Beams

The high beam headlamps receive voltage from the headlamp HI relay located in the underhood fuse block. The body control module (BCM) controls the relay on the headlamp high beam relay control circuit. High beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is grounded, the BCM grounds the headlamp high beam relay control circuit, illuminating the high beam headlamps. The right and left high beam circuits are independent and are fused independently in the underhood fuse block. The right and left headlamps are grounded at G100 and G104.

The high beam indicator is illuminated when the instrument cluster receives a class 2 serial data message from the BCM that the high beams are illuminated.

Low Beams

The low beam headlamps receive voltage from the headlamp LOW relay located in the underhood fuse block. The body control module (BCM) controls the relay on the headlamp low beam relay control circuit. Low beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is open, the BCM grounds the headlamp low beam relay control circuit, illuminating the low beam headlamps. The right and left low beam circuits are independent and are fused independently in the underhood fuse block. The right and left headlamps are grounded at G100 and G104.

Daytime Running Lamps (DRL)

The daytime running lamps (DRL) will operate when the ignition switch is in the RUN position, for automatic transmissions (A/T), the gear selector is not in the PARK position, the headlamp switch is in the AUTO position, and for manual transmissions (M/T), the park brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate. The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal it will either turn on the DRL or the headlamps for auto headlamp operation. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. The DRL can be manually turned OFF by depressing the AHL/DRL switch in the headlamp switch. The AHL/DRL defeat switch sends a ground signal through the DRL switch signal circuit to the BCM. The BCM then turns OFF the DRL and headlamps switch to manual control. When the AHL/DRL are manually turned OFF at the headlamp switch, the AHL/DRL will default to ON with the next ignition cycle. The DRL are separate lamps independent of the headlamps. With the headlight switch in the AUTO position, the DRL will either be turned ON or OFF, after an approximate 8-second delay depending on whether daylight or low light conditions are sensed. The DRL 10-amp fuse in the underhood fuse block supplies battery positive voltage to the DRL relay switch contacts and relay coil. When the BCM energizes the DRL relay, the DRL receive voltage on the DRL supply voltage circuit. Ground for the DRL is at G100.

Fog Lamps

With both the ignition switch in the RUN position, and the park lamps ON, the fog lights will illuminate when the driver depresses the fog lamp switch. The FOG LPS 15-amp fuse in the underhood fuse block supplies battery positive voltage to the fog lamp relay switch and coil. With the headlamp switch in either the park or headlamp position, and the fog lamp switch is in the ON position, the body control module (BCM) will energize the fog lamp relay control circuit. The BCM receives the park lamp ON signal from the interior park lamps supply voltage signal circuit. The current flow is from the fog lamp relay to both front fog lamps and to ground G100. The state of the fog lamps will remain the same until the fog lamp switch position is changed, or the ignition switch is cycled OFF and ON. Fog lamp operation will be cancelled whenever the park lamps, are turned OFF or the high beam headlights have been selected.

The rear fog lamps are controlled in much the same way, however the front fog lamps must be on in order to turn on the rear fog lamps. The SEO 1 15-amp fuse in the underhood fuse block supplies battery positive voltage to the rear fog lamp relay switch and coil. Both the relay control and current flow are the same as the front fog lamps with the exception of the rear fog lamp ground at G402.

Park, Tail and Marker Lamps

The park, tail and marker lamps, including the license lamps, are turned on when the headlamp switch is placed in the PARK or HEAD position or anytime the headlights are requested. The underhood fuse block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The body control module (BCM) provides a ground or control circuit to the park lamp relay coil circuit. When the park lamps are turned on the BCM energizes the park lamp relay. Current flow is from the park lamp relay to the FR PRK 10-amp fuse, RR PRK 10-amp fuse, LR PRK 10-amp fuse, and the TRL PRK 10-amp fuse, and to their respective park and marker lamps. The front park and marker lamps are grounded at G100. The rear park and marker lamps are grounded at G401. The license lamps are grounded at G410. If the headlight switch is left in the ON position, the inadvertent power control feature will turn off the park, tail and marker lamps approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park, tail and marker lamps will remain ON until turned OFF or the battery runs dead.

Exterior Courtesy Lamps

The body control module (BCM), driver door module (DDM), and the passenger door module (PDM) communicate through the class 2 serial data system. The DDM and the PDM supply power and ground to the left and right exterior lamps respectively. When the BCM commands illuminated entry, a command is also sent to the DDM/PDM for illumination of the exterior courtesy lamps. If the door locks are activated to the LOCK position, or if the ignition switch is turned to either the ON or RUN position the exterior courtesy lamps will deactivate immediately.

When an outside door handle is lifted or a door is opened, the exterior courtesy lamps illuminate.

Turn Signal/Hazard Lamps

The IGN E 10-amp fuse in the underhood fuse block supplies battery positive voltage to the turn signal/hazard switch assembly. The FLASH 25-amp fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the turn signal/flasher module and ground is supplied at G200. When the turn signal switch is placed in either the LEFT or RIGHT position, a voltage signal is completed from the turn signal switch to the turn sign/flasher module. When the hazard flasher switch is activated, a ground signal is completed from the turn signal/hazard switch to the turn sign/flasher module. The turn sign/flasher module then sends an on-off voltage signal through the LT TRLR, RT TRLR, LT TURN or RT TURN 10-amp fuses in the I/P fuse block to the appropriate turn signal or to all 4 fuses for hazard operation. The instrument panel cluster (IPC) indicators receive voltage from the LT TURN and RT TURN fuses as well as the driver door module (DDM)/passenger door module (PDM) for the mirror turn signals. The DDM/PDM has no function or control of the mirror turn signals other that a pass through connection for the circuits. The audio chime is also activated when the turn signals are ON. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G100. The rear turn signals are grounded at G401. The Mirror turn signals are grounded by the DDM/PDM.

Stop Lamps

The STOP LP 25-amp fuse in the underhood fuse block supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery positive voltage is supplied to both the STOP 15-amp fuse and the center high mounted stop lamp (CHMSL) 10-amp fuse in the instrument panel (I/P) fuse block, and to the turn signal/hazard module. The turn signal/hazard module then supplies voltage to both of the trailer rear turn/stop lamp supply voltage circuits. The voltage from the CHMSL 10-amp fuse is to the CHMSL and the trailer jumper harness. The voltage from the STOP 15-amp fuse is to the stop lamps, throttle actuator control (TAC) module, and the cruise control.

Backup Lamps - Automatic Transmission

The backup lamp request signal is sent from the powertrain control module (PCM) to the body control module (BCM) on the class 2 message system. This signal is based on the park/neutral position (PNP) switch signal. The BCM supplies voltage on the backup lamp supply voltage circuit to the backup lamps and to the automatic day/night mirror. Voltage for the courtesy lamp supply voltage circuit and backup lamp supply voltage circuit is from the TBC B fuse in the instrument panel (I/P) fuse block directly through the BCM to these circuits. A short to ground on either of these circuits will open the fuse. The backup lamps are grounded at G401.

For trailer wiring, a separate backup lamp circuit is connected through the underhood fuse block from the TRLR B/U 10-amp fuse to the trailer wiring harness.

Backup Lamps - Manual Transmission

The B/U LP 20-amp fuse in the underhood fuse block supplies battery positive voltage to the normally open park/neutral position (PNP) switch or backup lamp switch. When driver places the gear selector lever is in the REVERSE position, the switch closes and the voltage is from the switch to the body control module (BCM). The BCM supplies voltage on the backup lamp supply voltage circuit to the backup lamps and to the automatic day/night mirror. Voltage for the courtesy lamp supply voltage circuit and backup lamp supply voltage circuit is from the TBC B fuse in the instrument panel (I/P) fuse block directly through the BCM to these circuits. A short to ground on either of these circuits will open the fuse. The backup lamps are grounded at G401.

For trailer wiring, a separate backup lamp circuit is connected through the underhood fuse block from the TRLR B/U 10-amp fuse to the trailer wiring harness.

Cargo Lamps

The inadvertent power supply voltage circuit of the body control module (BCM) provides positive voltage to the cargo lamps. When the cargo lamp switch is pressed, the switch closes, ground is supplied to the cargo lamps, and the lamps illuminate. In the event that the cargo lamps were to remain on for a period of more than 10 minutes after the ignition switch is changed to the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition. Ground for the cargo lamps is supplied through the cargo lamp switch, from G203.

Clearance Lamps

The clearance lamps, are turned ON when the headlamp switch is placed in the PARK or HEAD position or anytime the headlamps are requested. The underhood fuse block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The body control module (BCM) provides a ground or control circuit to the park lamp relay coil circuit. When the park lamps are turned ON, the BCM energizes the park lamp relay. Current flow is from the park lamp relay to the INT PRK 10-amp fuse, and to the clearance and roof lamps. If the headlamp switch is left in the ON position, the inadvertent power control feature will turn OFF the park, tail and clearance lamps approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlamp switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park, tail and marker lamps will remain ON until turned OFF or the battery runs dead.

Roof Beacon Lamp

The roof beacon lamp will illuminate when the driver depresses the roof beacon lamp switch. The SEO B1 15-amp fuse in the underhood fuse block supplies battery positive voltage to the roof beacon switch. The SEO B2 30-amp fuse in the underhood fuse block supplies battery positive voltage to the roof beacon relay. When the switch is depressed, the roof beacon coil is energized and the roof beacon relay supplies voltage to the roof beacon lights. The roof beacon relay and roof beacon light is grounded at G304 except crewcab, and crewcab is grounded at G305.

Interior Lamps

The interior lighting consist of the following 2 groups. This first group includes lamps that may not be dimmed.

1. Courtesy/Illuminated entry lamps
2. Dome lamps
3. Map lamps
4. Reading lamps
5. Vanity mirror lamps

Courtesy/Illuminated Entry Lamps

The courtesy/illuminated entry lamps, may be manually turned on or off by placing the interior lamp switch in the ON or OFF position. If an outside door handle is lifted or a door is opened, the courtesy/illuminated entry lamps illuminate. After all the doors have been closed the courtesy/illuminated entry lamps will remain illuminated approximately 15 seconds. The courtesy/illuminated entry lamps will also turn on prior to any door being opened, and remain illuminated approximately 40 seconds when the driver removes the ignition key. When the driver places the dome lamp defeat switch in the OFF position, the courtesy/illuminated entry lamps will be disabled.

The left and right front door courtesy lamps are controlled, and receive voltage and ground from the drivers door module (DDM) and the passenger door module (PDM) respectively. The body control module (BCM), DDM, and the PDM communicate through class II serial data for the lamp illumination commands and the door ajar switches.

The remaining courtesy lamps are controlled and receive voltage from the BCM. Voltage for the courtesy lamp supply voltage circuit and the backup lamp supply voltage circuit is from the TBC B fuse in the instrument panel fuse block directly through the BCM to these circuits. A short to ground on either of these circuits will open the fuse. Ground is provided to the footwell lamps and all courtesy/reading lamps at G203. Ground is provided to the right middle and right rear door at G306. Ground is provided to the left middle and left rear door at G302.

Keyless Entry Interior Illumination

When the driver uses the door key in order to unlock the doors, the BCM receives a door unlock signal. The BCM must have inputs that indicate that the ignition switch is OFF, the courtesy lamp switch is OFF and all the doors are closed. The BCM will then activate the interior lamps. The courtesy lamps will remain on, approximately 15 seconds after the door is closed. The BCM will then turn them off through the theater dimming feature. If the door locks are activated to the LOCK position, or if the ignition switch is turned to either the RUN or CRANK position the courtesy lamps will turn off immediately.

When the driver uses the remote function actuator transmitter to unlock the doors, trunk or presses the panic button, the BCM will keep the courtesy lamps on approximately 40 seconds. When the driver uses the remote function actuator transmitter to lock the doors, the BCM will keep the courtesy lamps on approximately 2 seconds. If the ignition switch is turned to either the RUN or CRANK position the courtesy lamps will turn off immediately. The BCM will also keep the courtesy lamps on approximately 40 seconds, after an alarm event is completed.

Vanity Lamps

The inadvertent power supply voltage circuit of the BCM provides battery positive voltage to each vanity mirror lamp. When the vanity mirror cover on the sunshade is opened, a switch closes to provide a ground circuit and the vanity lamp illuminates. In the event that any of these lamps were to remain illuminated for a period of more than 10 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition. Ground is provided to the vanity lamps at G203.

Reading Lamps

The inadvertent power supply voltage circuit of the BCM provides battery positive voltage to the reading lamps. The reading lamps and switch are integral to the courtesy/reading lamp assembly. When the switch is closed, voltage is supplied and the lamp illuminates. In the event that any of these lamps were to remain illuminated for a period of more than 10 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition. Ground is provided to the reading lamps at G203.

Battery Rundown Protection/Inadvertent Power

The BCM inadvertent power supply voltage circuit provides battery positive voltage to all of the interior reading lamps, visor vanity mirror lamps, and the cargo lamps. In the event that any of these lamps were to remain illuminated for a period of more than 10 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition.

The BCM also utilizes the inadvertent power supply voltage circuit as a lamp request when none of the lamps in the circuit are illuminated. When a lamp switch is activated, the BCM receives the request for lamp illumination and switches to supplying voltage to the inadvertent power supply voltage circuit.

Interior Lamps Dimming

The second group includes lamps which may be dimmed. This group may use a combination of vacuum fluorescent (VF) illumination and incandescent lamps.

When the ignition switch is turned to the RUN position, the radio's vacuum fluorescent (VF) displays turn on at maximum brightness. When the park lamps are on, all incandescent back lighting turn on at the dimming level indicated by the I/P dimmer switch. At the same time all vacuum fluorescent (VF) displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the BCM. When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all vacuum fluorescent (VF) displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.

The following switches and components have back lighting when the park lamps are on

1. The instrument panel cluster (IPC)
2. Radio, front and rear
3. Window and heated seat switches
4. Garage door opener switch
5. Selectable ride switch
6. Roof beacon switch
7. Power take off (PTO) switch
8. Headlamp leveling switch
9. Rear wheel steering mode select switch
10. HVAC control assembly
11. Headlamp and panel dimmer switch
12. Transfer case shift control switch
13. PSIR disable switch
14. PRNDL lamps
15. Traction control switch
16. Steering wheel control switches
17. Fog lamp switches

The left and right front door switch illumination is controlled, receives voltage and ground from the drivers door module (DDM) and the passenger door module (PDM) respectively. The radio is also a class II module and has full control of its illumination. The BCM, DDM, PDM, and radio communicate through class II serial data for the lamp illumination commands

The I/P cluster illumination lamps receive voltage and are controlled by the BCM on the instrument panel lamps dimming supply voltage circuit. Ground for the instrument panel lamps is at G203.

The various switches, HVAC control assembly, and the PRNDL lamps receive voltage and are controlled by the BCM on the instrument panel lamps dimming control circuit. Ground for the rear window switches is at G302 and G306. Ground for the traction control switch, steering wheel controls, and the rear window/wiper switch is at G108. Ground for the remaining switches is at G203.

The following indicators receive voltage from the BCM and are controlled by ground or from various modules

1. Rear wheel steering mode select switch indicators
2. Fog lamp switch indicators
3. All multifunction accessory switch indicators
4. Selectable ride switch
5. Roof beacon
6. Traction control switch traction control OFF indicator
7. Transfer case control switch position indicators

Ground/control for the indicators is from various modules or ground. Voltage for the LED dimming supply circuit, instrument panel lamps dimming control circuit and the instrument panel lamps dimming supply circuit is from the TBC A fuse in the instrument panel fuse block directly through the BCM to these circuits. A short to ground on only the instrument panel lamps dimming control circuit will open the fuse.

The modules controlling the above indicators are as follows

1. Rear wheel steering control module
2. Electronic suspension control module
3. Transfer case shift control module
4. Body control module (BCM)