Dodge Ram Truck 1500-2500-3500. Manual — part 433

LAMP

1. Check to be certain that the three front lamp unit

U-nuts (1) are properly positioned on the fender.

2. Position the front lamp unit (1) close enough to the

front fender to access and reconnect the park and
turn signal lamp wire harness connection (3) to the
park and turn signal bulb socket (2) on the back of
the lamp housing.

3. Reconnect the headlamp wire harness connection

(4) to the headlamp bulb socket (5) on the back of
the lamp housing.

8L - 138

LAMPS/LIGHTING - EXTERIOR - SERVICE INFORMATION

DR/DH

4. Position the front lamp unit (5) to the fender panel

opening.

5. Rearrange the wire harness (1) as necessary to

prevent it from becoming pinched between the
back of the lamp housing and the fender.

6. Insert the two alignment pins on the back of the

lamp housing into the two alignment holes in the
fender lamp mounting panel and, using hand pres-
sure, push the lamp into the fender until it is fully
seated.

7. Install and tighten the three screws (4) that secure

the lamp to the U-nuts on the fender ledge in the
following sequence: outboard screw, inboard lower
screw, inboard upper screw. Tighten the screws to
7 N·m (65 in. lbs.).

8. Engage the three plastic retainers (3) that secure

the rubber welt (2) on the inboard side of the lamp
to the holes in the fender ledge.

9. Reconnect the battery negative cable.

10. Confirm proper headlamp alignment. (Refer to 8 - ELECTRICAL/LAMPS/LIGHTING - EXTERIOR - STANDARD

PROCEDURE - FRONT LAMP AIMING).

SWITCH-HEADLAMP

DESCRIPTION

The headlamp switch (1) is located on the instrument
panel, to the left of the steering column. Two different
switches are used. The standard switch features a
three-position rotary knob (3) for exterior lighting con-
trol and a thumbwheel (2) for panel lamps dimming
and interior lighting control. An optional switch has the
same thumbwheel, but has an additional “Pull” func-
tion added to the rotary knob for selecting the optional
front fog lamps.

Each of these switches is constructed of molded plas-
tic. The rotary knob is molded plastic and has a raised
center lever to ease operator control. The thumbwheel
is also plastic and knurled. The optional front fog lamp
rotary knob is plastic with a smooth finish and an
International Control and Display Symbol icon for
“Front Fog Light” applied to it. The switch face plate is
also labeled with graphics and icons to clearly identify
the

many

functions

of

the

rotary

knob

and

thumbwheel.

Three screws secure the switch to the back of the cluster bezel through integral mounting flanges that are molded
to each side of the switch housing. The back of the switch housing has an integral connector receptacle containing
terminal pins that connect the switch to the vehicle electrical system through a dedicated take out and connector of
the instrument panel wire harness. A panel dimmer controlled incandescent bulb soldered to the circuit board within
the switch provides back lighting for visibility at night, but is not serviceable. The headlamp switch cannot be
repaired and, if faulty or damaged, it must be replaced.

DR/DH

LAMPS/LIGHTING - EXTERIOR - SERVICE INFORMATION

8L - 139

OPERATION

The headlamp switch uses two resistor multiplexed outputs to control the many functions and features it provides.
The switch receives a clean ground from the ElectroMechanical Instrument Cluster (EMIC) (also sometimes referred
to as the Cab Control Node/CCN) on a headlamp switch return circuit. It then provides outputs to the EMIC on a
headlamp switch signal circuit to control exterior lighting functions, and on a panel lamps dimmer signal circuit to
control panel dimmer and interior lighting functions.

The switch illumination circuit receives a path to ground at all times through the left instrument panel ground circuit.
The illumination level is controlled by a Pulse-Width Modulated (PWM) output received from the EMIC on a head-
lamp switch illumination control circuit. The EMIC controls this output based upon the dimmer signal select mux
input from the headlamp switch.

The headlamp switch operates as follows:

•

Front Fog Lamps Control - For vehicles so equipped, the rotary knob on the headlamp switch is pulled out
to activate or pushed in to deactivate the optional front fog lamps. The headlamp switch provides an output to
the EMIC, and the EMIC responds by sending electronic fog lamp switch status messages to the Front Control
Module (FCM) over the Programmable Communications Interface (PCI) data bus. The FCM responds by ener-
gizing or de-energizing the front fog lamp relay in the Power Distribution Center (PDC).

•

Exterior Lighting Control - The rotary knob on the headlamp switch is rotated to a detent position to activate
or deactivate the exterior lighting. The headlamp switch provides an output to the EMIC, and the EMIC
responds by sending electronic exterior lighting switch status messages to the FCM over the PCI data bus.
The FCM responds by energizing or de-energizing the park lamp relay in the PDC and the high or low beam
headlamp circuits. The FCM remembers which headlamp beams were last selected using the multi-function
switch, and energizes those beams by default the next time the headlamps are turned On.

•

Interior Lighting Control - The thumbwheel on the headlamp switch is rotated to the dome defeat, dome on,
parade/funeral mode, or one of the six panel dimmer detent positions to control the interior courtesy/dome and
panel lamps. The headlamp switch provides an output to the EMIC, and the EMIC responds by providing the
appropriate interior lighting control outputs through its internal courtesy lamp driver circuits, electronic dimming
level messages to other modules over the PCI data bus, and/or the proper PWM outputs to control dimming
levels through several panel dimmer illumination control driver circuits.

The headlamp switch can be diagnosed using conventional diagnostic tools and methods. However, proper testing
of the multiplexed inputs to and PWM processing of the EMIC requires the use of a diagnostic scan tool. Refer to
the appropriate diagnostic information.

DIAGNOSIS AND TESTING

HEADLAMP SWITCH

WARNING: To avoid personal injury or death, on vehicles equipped with airbags, disable the supplemental
restraint system before attempting any steering wheel, steering column, airbag, seat belt tensioner, impact
sensor, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative
(ground) cable, then wait two minutes for the system capacitor to discharge before performing further diag-
nosis or service. This is the only sure way to disable the supplemental restraint system. Failure to take the
proper precautions could result in accidental airbag deployment.

8L - 140

LAMPS/LIGHTING - EXTERIOR - SERVICE INFORMATION

DR/DH

1. Remove the left bezel and the headlamp switch

from the instrument panel as a unit. (Refer to 23 -
BODY/INSTRUMENT

PANEL/INSTRUMENT

PANEL SWITCH BEZEL - REMOVAL).

2. Disconnect the instrument panel wire harness con-

nector from the back of the headlamp switch.

3. Using an ohmmeter, test the resistance or continu-

ity between the terminals of the switch as shown in
the Headlamp Switch Tests table.

HEADLAMP SWITCH TESTS

SWITCH POSITION (PINS)

RESISTANCE RANGE (OHMS)

OFF (7 & 8)

4484.70 - 4575.30

HEADLAMP (7 & 8)

1089.00 - 1111.00

PARK (7 & 8)

584.10 - 595.90

FOG LAMP - HEADLAMP (7 & 8)

416.39 - 424.81

FOG LAMP - PARK (7 & 8)

312.94 - 319.26

DOME DEFEAT (6 & 7)

4593.60 - 4686.40

PANEL DIMMER 1 (6 & 7)

1316.70 - 1343.30

PANEL DIMMER 2 (6 & 7)

797.94 - 814.06

PANEL DIMMER 3 (6 & 7)

530.64 - 541.36

PANEL DIMMER 4 (6 & 7)

371.25 - 378.75

PANEL DIMMER 5 (6 & 7)

264.33 - 269.67

PANEL DIMMER 6 (6 & 7)

185.13 - 188.87

PARADE/FUNERAL MODE (6 & 7)

128.70 - 131.30

DOME ON (6 & 7)

85.73 - 87.47

CARGO (6 & 7)

51.78 - 52.82

SWITCH ILLUMINATION (3 & 4)

CONTINUITY AT ALL TIMES

FOG LAMP INDICATOR (4 & 5)

CONTINUITY AT ALL TIMES

4. If the switch fails any of the tests, replace the faulty headlamp switch as required.

REMOVAL

WARNING: To avoid personal injury or death, on vehicles equipped with airbags, disable the supplemental
restraint system before attempting any steering wheel, steering column, airbag, seat belt tensioner, impact
sensor, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative
(ground) cable, then wait two minutes for the system capacitor to discharge before performing further diag-
nosis or service. This is the only sure way to disable the supplemental restraint system. Failure to take the
proper precautions could result in accidental airbag deployment.

DR/DH

LAMPS/LIGHTING - EXTERIOR - SERVICE INFORMATION

8L - 141