Lamps/Lighting - Interior

The interior lighting system for this model includes incandescent lighting on two separate circuits: the dome/courtesy lamp circuit and the panel lamps dimmer circuit. The lamps on the dome/courtesy circuit include:
- Cargo Lamps (5) - The standard equipment cargo lamps are integral to the Center High Mounted Stop Lamp (CHMSL) located on the roof rear header above the rear glass on the back of the cab. One cargo lamp bulb is behind a clear lens on each outboard side of the center red lens of the CHMSL. The cargo lamps are manually activated by selecting a detent position of the panel lamps dimmer thumbwheel of the headlamp switch on the instrument panel to illuminate the cargo area of the pick-up box.
- Dome/Reading Lamps (Overhead Console) (3) - In vehicles equipped with an optional overhead console there are two dome/reading lamps that are integral to the overhead console, which is centered in the headliner near the windshield header. The overhead console lamps have switches that are individually actuated by depressing their respective lamp lenses.
- Front Dome Lamp (5 - Standard Cab or 3 - Quad Cab) - On standard cab models the dome lamp is centered in the headliner near the back of the cab. On quad cab models the front dome lamp is centered in the headliner near the windshield header. The standard (base) dome lamp has a single bulb and is switched by the door ajar switches or the interior lighting thumbwheel of the headlamp switch. The optional dome/reading lamps are mounted in the same location but include an integral switch that is actuated by depressing the lamp lens.
- Glove Box Lamp (1) - A standard glove box lamp with an integral switch is located at the upper right corner of the instrument panel glove box opening and illuminates whenever the glove box is opened.
- Rear Dome/Reading Lamp (Quad Cab Only) (4 - Without Sunroof or 5 - With Sunroof) - The rear dome/ reading lamp on quad cab models includes a single bulb and a switch that is actuated by depressing the lamp lens. In vehicles without an optional sunroof the rear dome/reading lamp is located in the center of the headliner between the front and rear seating. On vehicles with a sunroof the dome/reading lamp is centered in the headliner near the back of the cab.
- Vanity Lamps (2) - Optional single intensity vanity lamps are located on each side of a covered mirror on both the right and left sun visors, and are controlled by an integral vanity mirror cover-actuated switch.

Most controls on the instrument panel and other controls located elsewhere on the interior of the vehicle are illuminated for night visibility. Some have miniature incandescent bulbs or Light-Emitting Diode (LED) units that are soldered to internal circuit boards and are not serviceable. The replaceable incandescent bulbs or bulb/bulb holder units in this vehicle include:
- Compass Mini-Trip Control Illumination Lamps - The optional Compass Mini-Trip Computer (CMTC) has three replaceable bulb/bulb holder units to illuminate its controls.
- Heater-Air Conditioner Control Illumination Lamps - The heater-air conditioner control panel has two replaceable bulb/bulb holder units to illuminate its controls.

Other components of the interior lighting system for this model include:
- Door Ajar Switches - A door ajar switch is integral to the door latch mechanism of each front and rear door.
- 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 vertical thumbwheel for selecting the panel lamps dimming level and for interior lighting control. A Parade position of the thumbwheel illuminates all Vacuum Fluorescent Display (VFD) units at full brightness for visibility when driving in daylight with the exterior lighting turned On. There are also detent positions to turn on all interior courtesy lighting, to turn on the rear cargo lamps, and a Defeat position that overrides door ajar switch control of interior lighting.
- 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.

Hard wired circuitry connects the interior 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 interior 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.

The interior lighting systems can be divided into two general classifications based upon the circuit that controls their operation: The courtesy lamp circuit, or the panel lamps dimmer circuit. The hard wired circuits and components of the interior lighting systems may be diagnosed and tested using conventional diagnostic tools and methods. However, conventional diagnostic methods may not prove conclusive in the diagnosis of the ElectroMechanical Instrument Cluster (EMIC), or the Programmable Communications Interface (PCI) data bus. The most reliable, efficient, and accurate means to diagnose the EMIC, the PCI data bus, or the electronic bus message inputs and outputs related to the various interior lighting systems requires the use of a diagnostic scan tool.

COURTESY LAMP CIRCUIT
Depending upon the selected vehicle options the courtesy lamp circuit may include the dome and dome/reading lamps located in the headliner near the windshield and between the front and rear seating, the cargo lamps located near the center of the rear roof header, the glove box lamp in the top of the glove box opening in the instrument panel, and the vanity lamps located in the sun visors. The lamps in the courtesy lamp circuit are provided with a path to ground at all times. The EMIC controls the output of battery voltage for the courtesy lamps in this circuit based upon hard wired inputs from the door ajar switches, the headlamp switch and the ignition switch.

After all of the ajar switch inputs to the EMIC transition to open, the EMIC will keep the courtesy lamps illuminated for about 30 seconds, then fade the lamps to off (theater dimming) over about three seconds. The EMIC also provides courtesy lamp operation based upon a resistor multiplexed input from the vertical thumbwheel on the headlamp switch, and provides an illuminated entry feature in response to certain electronic message inputs received from the Remote Keyless Entry (RKE) module and the Airbag Control Module (ACM) over the PCI data bus. A resistor multiplexed courtesy lamp defeat input from the vertical thumbwheel of the headlamp switch will cause the EMIC to override normal courtesy lamp operation based upon inputs from all of the ajar switches.

For those lamps on the courtesy lamp circuit with independent switching such as the optional switched dome lamp, the optional dome/reading lamps, the optional vanity lamps, and for the glove box lamp the EMIC provides a battery voltage output to the switches through a separate circuit. The EMIC provides a battery saver (load shedding) feature for all courtesy lamps, which will automatically turn these lamps off if they are left on for more than about eight minutes with the ignition switch in the Off position.

PANEL LAMPS DIMMER CIRCUIT
The panel lamps dimmer circuit actually includes several circuits. These circuits control the illumination and dimming level of the headlamp switch, the heater-air conditioner controls and the four-wheel drive selector switch. All lamps in the panel lamps dimmer circuits are provided a path to ground at all times through a hard wired ground circuit. These lamps illuminate based upon inputs to the EMIC from the rotary control knob and vertical thumbwheel of the headlamp switch. The control knob on the headlamp switch selects the exterior lights, while the thumbwheel selects the panel lamps intensity (dimming) level.

When the exterior lighting is turned On, the EMIC provides electronic dimming level messages to the radio and the Compass Mini-Trip Computer (CMTC) over the PCI data bus. The EMIC also supplies a 12-volt Pulse Width Modulated (PWM) output to all of the incandescent lamps in the panel lamps dimmer circuits through several panel lamps dimmer circuits. This shared PWM output synchronizes the selected illumination intensity level of all of the lamps in the panel lamps dimmer circuit.

The radio and the CMTC each use the dimming level messages to control the illumination intensity of both their Vacuum Fluorescent Display (VFD) units and their control lighting. In addition, when the thumbwheel of the headlamp switch is moved to the Parade/Funeral Mode detent position, all of the VFD units are illuminated at their full intensity levels for increased visibility when the vehicle is driven during daylight hours with the exterior lights turned On.