1998 DODGE RAM 1500 trailer

²Engine loads and temperatures are high such as
when towing a trailer.
²Cool silicone fluid within the fan drive unit is
being redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
LEAKS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. If leakage appears
excessive, replace the fan drive unit.
VISCOUS DRIVE
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when
spun by hand), replace the fan drive. This spin test
must be performed when the engine is cool.
For the following test, the cooling system must be
in good condition. It also will ensure against exces-
sively high coolant temperature.
WARNING: BE SURE THAT THERE IS ADEQUATE
FAN BLADE CLEARANCE BEFORE DRILLING.
(1) Drill a 3.18-mm (1/8-in) diameter hole in the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). It should have a range of -18É-to-
105ÉC (0É-to-220É F). Insert thermometer through the
hole in the shroud. Be sure that there is adequate
clearance from the fan blades.
(3) Connect a tachometer and an engine ignition
timing light. The timing light is to be used as a
strobe light. This step cannot be used on the diesel
engine.(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator. Use tape at
the top to secure the plastic and be sure that the air
flow is blocked.
(5) Be sure that the air conditioner (if equipped)
and blowe fan is turned off.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
(6) Start the engine and operate at 2400 rpm.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 88É C (190É F).
Fan driveengagementshould start to occur at/be-
tween:
²3.7L Automatic - 93É C - 99ÉC (200É F - 210É F)
²3.7L Manual/4.7L Automatic/5.9L - 85É - 91É C
(185É - 195É F)
²4.7L Manual - 74É - 79É C (165É - 175É F)
²5.7L
²5.9L
²Engagement is distinguishable by a definite
increasein fan flow noise (roaring). The timing light
also will indicate an increase in the speed of the fan.
(7) When viscous drive engagement is verified,
remove the plastic sheet. Fan drivedisengagement
should start to occur at or between:
²3.7L Automatic - 76ÉC - 81ÉC (168É F - 178É F)
²3.7L Manual/4.7L Auto/ 5.9L - 67ÉC - 73ÉC (153É
F - 163É F)
²4.7L Manual - 56ÉC - 62ÉC (133É F - 143É F)
²5.7L
²5.9L
²8.0L engine - 93É to 101É C (190É - 205É F) Min-
imum 73ÉC (163ÉF). A definitedecreaseof fan flow
noise (roaring) should be noticed. If not, replace the
defective viscous fan drive unit.
CAUTION: Some engines equipped with serpentine
drive belts have reverse rotating fans and viscous
fan drives. They are marked with the word
REVERSE to designate their usage. Installation of
the wrong fan or viscous fan drive can result in
engine overheating.
Fig. 32 Viscous Fan Drive - Typical
1 - VISCOUS FAN DRIVE
2 - THERMOSTATIC SPRING
3 - MOUNTING NUT TO WATER PUMP HUB
DRENGINE 7 - 51
FAN DRIVE VISCOUS CLUTCH-GAS ENGINES (Continued)

CAUTION: If the viscous fan drive is replaced
because of mechanical damage, the cooling fan
blades should also be inspected. Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration. Replace fan
blade assembly if any of these conditions are
found. Also inspect water pump bearing and shaft
assembly for any related damage due to a viscous
fan drive malfunction.
FAN DRIVE VISCOUS CLUTCH
- 5.9L DIESEL
DESCRIPTION
The electronically controlled viscous fan drive (Fig.
34) and (Fig. 33)is attached to the fan drive pulley
mounted to the engine. The coupling allows the fan
to be driven in a normal manner. The fan speed is
controlled by the electronic control module.
OPERATION
The Engine Control Module (ECM) controls the
level of engagement of the electronically controlled
viscous fan clutch by monitoring coolant tempera-
ture, intake manifold temperature, and air condition-
ing status. Based on cooling requirements, the ECMsends a signal to the viscous fan clutch to increase or
decrease the fan speed.
Fan speed is monitored by the ECM. Fan speeds
above or below a calibrated threshold will set a DTC.
Circuit concerns will also set fan clutch DTC's.
DIAGNOSIS AND TESTING - ELECTRONICALLY
CONTROLLED VISCOUS FAN DRIVE
NOISE
NOTE: It is normal for fan noise to be louder (roar-
ing) when:
²Fan duty cycle high. This may occur when ambi-
ent (outside air temperature) is very high.
²Engine loads and temperatures are high such as
when towing a trailer.
²Aggressive engine braking down a steep grade
where transmission temperatures may be high
²Cool silicone fluid within the fan drive unit is
being redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
Fig. 33 Electronically Controlled Viscous Drive
1 - ELECTRONICALLY CONTROLLED VISCOUS FAN DRIVE
2 - MOUNTING NUT
3 - WIRING SUPPORT BRACKET
4 - ELECTRICAL CONNECTOR
Fig. 34 Fan Blade/Viscous Fan Drive - 5.9L Diesel
Engine
1 - ELECTRICAL CONNECTOR
2 - VISCOUS FAN DRIVE
3 - FAN BLADE
4 - BOLT (6)
5 - RADIATOR FAN PULLEY
7 - 52 ENGINEDR
FAN DRIVE VISCOUS CLUTCH-GAS ENGINES (Continued)

MARKER LAMP UNIT
REMOVAL
REMOVAL - FENDER MARKER LAMP......17
REMOVAL - TAILGATE MARKER LAMP.....18
INSTALLATION
INSTALLATION - FENDER MARKER LAMP . . 18
INSTALLATION - TAILGATE MARKER LAMP . 18
MULTI-FUNCTION SWITCH
DESCRIPTION - TURN SIGNAL SYSTEM.....18
OPERATION - TURN SIGNAL SYSTEM.......18
DIAGNOSIS AND TESTING - MULTI-
FUNCTION SWITCH...................18
REMOVAL.............................19
INSTALLATION.........................19
PARK LAMP RELAY
DESCRIPTION.........................20
OPERATION...........................20
DIAGNOSIS AND TESTING - PARK LAMP
RELAY..............................20
REMOVAL.............................21
INSTALLATION.........................21
PARK/TURN SIGNAL LAMP
REMOVAL.............................21
INSTALLATION.........................21
TAIL LAMP
REMOVAL
REMOVAL - WITH CARGO BOX..........22REMOVAL - WITHOUT CARGO BOX.......22
INSTALLATION
INSTALLATION - WITH CARGO BOX.......22
INSTALLATION - WITHOUT CARGO BOX . . . 22
TAIL LAMP UNIT
REMOVAL
REMOVAL - WITH CARGO BOX..........22
REMOVAL - WITHOUT CARGO BOX.......23
INSTALLATION
INSTALLATION - WITH CARGO BOX.......23
INSTALLATION - WITHOUT CARGO BOX . . . 23
TRAILER TOW WIRING
DESCRIPTION.........................24
TURN LAMP
REMOVAL
REMOVAL - WITH CARGO BOX..........24
REMOVAL - WITHOUT CARGO BOX.......24
INSTALLATION
INSTALLATION - WITH CARGO BOX.......24
INSTALLATION - WITHOUT CARGO BOX . . . 24
UNDERHOOD LAMP
REMOVAL.............................25
INSTALLATION.........................25
UNDERHOOD LAMP UNIT
REMOVAL.............................25
INSTALLATION.........................25
LAMPS/LIGHTING - EXTERIOR
DESCRIPTION
The exterior lighting system for this model include
the following components:
²Backup Lamps
²Brake Lamps
²Daytime Running Lamps
²Front Fog Lamps
²Hazard Warning Lamps
²Headlamps
²Park Lamps
²Turn Signal Lamps
Other components of the exterior lighting system
for this model include:
²Backup Lamp Switch
²Brake Lamp Switch
²Front Control Module
²Front Fog Lamp Relay
²Hazard Switch
²Multi-Function Switch
²Park Lamp Relay
²Trailer Tow Connectors
Some of the interior and exterior lighting functions
are governed by the front control module. The head-
lamp, dome, and door ajar switchs provide signals to
the instrument cluster. The instrument cluster sends
a J1850 message to the front control module to
enable the necessary components for illumination.Hard wired circuitry connects the exterior lighting
system components to the electrical system of the
vehicle. Refer to the appropriate wiring information.OPERATION
DAYTIME RUNNING LAMPS
Power is reduced using pulse-width modulation to
the high beams, where by the power is switched on
and off rapidly instead of remaining on continuously.
The duration and interval of the power pulses is pro-
grammed into the Front Control Module (FCM).
HEADLAMP SYSTEM
The instrument cluster monitors both the multi-
plexed headlamp and multifunction switches. The
instrument cluster transmits a J1850 bus message to
the front control module (FCM) to activate the head-
lamps. The headlamp system will default to head-
lamps ON position when ignition switch is ON and
when an open or short circuit failure occurs on the
headlamp switch input to the instrument cluster. The
system will return to normal operation when the
open or short is repaired. A fault will be reported by
the Instrument Cluster when a failure occurs on the
dimmer or headlamp switch input.
If the exterior lamps are ON, and the headlamp
switch is in any position other than OFF, with the
ignition switch OFF (LOCK) after 5 minutes, the
8L - 2 LAMPS/LIGHTING - EXTERIORDR

REMOVAL - WITHOUT CARGO BOX
(1) Disconnect and isolate the negative battery
cable.
(2) Disconnect the body wire harness connector
from the tail lamp wire harness connector (Fig. 22).
(3) Remove the tail lamp unit connector from the
frame rail.
(4) Remove the two nuts that secure the tail lamp
housing to the mounting bracket.
(5) Remove the tail lamp unit from the mounting
bracket while routing the wire harness through the
bracket.
INSTALLATION
INSTALLATION - WITH CARGO BOX
(1) Connect the body wire harness connector to the
lamp back plate connector.
(2) Position the tail lamp unit into the cargo box.(3) Install the two screws that secure the tail lamp
unit to the cargo box.
(4) Raise the tailgate.
(5) Reconnect the negative battery cable.
INSTALLATION - WITHOUT CARGO BOX
(1) Position the tail lamp unit onto the mounting
bracket while routing the wire harness through the
bracket.
(2) Install the two nuts that secure the tail lamp
housing to the mounting bracket.
(3) Connect the tail lamp wire harness connector
to the body wire harness connector.
(4) Install the tail lamp connector retainer to the
frame rail.
(5) Reconnect the negative battery cable.
Fig. 21 Tail Lamp Unit
1 - SCREW (2)
2 - WIRE HARNESS CONNECTOR
3 - TAIL LAMP UNIT
Fig. 22 Tail Lamp Unit - RH Side Shown, LH Side
Typical
1 - TAIL LAMP UNIT
2 - MOUNTING BRACKET
3 - TRAILER HITCH BRACKET
4 - WIRE HARNESS
5 - NUT (2)
DRLAMPS/LIGHTING - EXTERIOR 8L - 23
TAIL LAMP UNIT (Continued)

TRAILER TOW WIRING
DESCRIPTION
Vehicles equipped with an optional factory-in-
stalled trailer towing package have a rear body wire
harness that includes an integral trailer tow wiring
take out that connects to a heavy duty, sealed, 7-pin
trailer tow connector located in the rear bumper (Fig.
23). This harness includes an adapter harness that
adapts the 7-pin trailer tow connector to a standard,
light-duty, 4-pin trailer tow connector. Refer to the
appropriate wiring information.
TURN LAMP
REMOVAL
REMOVAL - WITH CARGO BOX
(1) Disconnect and isolate the negative battery
cable.
(2) Remove the tail lamp unit (Refer to 8 - ELEC-
TRICAL/LAMPS/LIGHTING - EXTERIOR/TAIL
LAMP UNIT - REMOVAL).
(3) Remove the lamp back plate from the tail lamp
unit.
(4) Release the turn signal bulb locking tabs and
remove the bulb from the back plate.
REMOVAL - WITHOUT CARGO BOX
(1) Disconnect and isolate the negative battery
cable.(2) Remove the four screws that secure the tail
lamp lens to the tail lamp housing (Fig. 24).
(3) Separate the tail lamp lens from the tail lamp
housing.
(4) Push the turn signal bulb inward and rotate it
counter-clockwise.
(5) Remove the turn signal bulb from the tail lamp
socket.
INSTALLATION
INSTALLATION - WITH CARGO BOX
(1) Install the turn signal bulb into the lamp back
plate.
(2) Install the lamp back plate onto the tail lamp
unit.
(3) Install the tail lamp unit (Refer to 8 - ELEC-
TRICAL/LAMPS/LIGHTING - EXTERIOR/TAIL
LAMP UNIT - INSTALLATION).
(4) Reconnect the negative battery cable.
INSTALLATION - WITHOUT CARGO BOX
(1) Install the turn signal bulb into the tail lamp
socket by pushing inward and rotating it clockwise.
NOTE: Install the tail lamp lens with the clear por-
tion (back-up lens) at the top of the housing. Make
sure that the gasket is correctly in place and not
twisted or torn.
(2) Position the tail lamp lens and gasket onto the
tail lamp unit.
NOTE: Do not overtighten the tail lamp lens screws
or damage to the tail lamp lens may result.
(3) Install the four screws that secure the tail
lamp lens to the tail lamp unit. Tighten the screws
securely.
(4) Reconnect the negative battery cable.
Fig. 23 Trailer Tow Wiring
1 - RETAINER CLIP (4)
2 - REAR BODY HARNESS (TRAILER TOW TAKE OUT)
3 - RETAINER CLIP (2)
4 - WIRE HARNESS CONNECTOR
Fig. 24 Tail Lamp Lens
8L - 24 LAMPS/LIGHTING - EXTERIORDR

WIRING
TABLE OF CONTENTS
page page
WIRING DIAGRAM INFORMATION....... 8W-01-1
COMPONENT INDEX.................. 8W-02-1
POWER DISTRIBUTION............... 8W-10-1
GROUND DISTRIBUTION.............. 8W-15-1
BUS COMMUNICATIONS.............. 8W-18-1
CHARGING SYSTEM.................. 8W-20-1
STARTING SYSTEM.................. 8W-21-1
FUEL/IGNITION SYSTEM.............. 8W-30-1
TRANSMISSION CONTROL SYSTEM..... 8W-31-1
VEHICLE SPEED CONTROL............ 8W-33-1
REAR WHEEL ANTILOCK BRAKES....... 8W-34-1
ALL WHEEL ANTILOCK BRAKES........ 8W-35-1
VEHICLE THEFT SECURITY SYSTEM..... 8W-39-1
INSTRUMENT CLUSTER............... 8W-40-1
HORN/CIGAR LIGHTER/POWER OUTLET . . 8W-41-1
AIR CONDITIONING.................. 8W-42-1
AIRBAG SYSTEM.................... 8W-43-1
INTERIOR LIGHTING.................. 8W-44-1AUDIO SYSTEM..................... 8W-47-1
REAR WINDOW DEFOGGER............ 8W-48-1
OVERHEAD CONSOLE................. 8W-49-1
FRONT LIGHTING.................... 8W-50-1
REAR LIGHTING..................... 8W-51-1
TURN SIGNALS...................... 8W-52-1
WIPERS............................ 8W-53-1
TRAILER TOW....................... 8W-54-1
NAVIGATION/TELECOMMUNICATION..... 8W-55-1
POWER WINDOWS................... 8W-60-1
POWER DOOR LOCKS................ 8W-61-1
POWER MIRRORS................... 8W-62-1
POWER SEATS...................... 8W-63-1
SPLICE INFORMATION................ 8W-70-1
CONNECTOR PIN-OUTS............... 8W-80-1
CONNECTOR/GROUND/SPLICE
LOCATION........................ 8W-91-1
POWER DISTRIBUTION............... 8W-97-1 DRWIRING 8W - 1

DESCRIPTION - CIRCUIT FUNCTIONS
All circuits in the diagrams use an alpha/numeric
code to identify the wire and it's function. To identify
which circuit code applies to a system, refer to the
Circuit Identification Code Chart. This chart shows
the main circuits only and does not show the second-
ary codes that may apply to some models.
CIRCUIT IDENTIFICATION CODE CHART
CIRCUIT FUNCTION
A BATTERY FEED
B BRAKE CONTROLS
C CLIMATE CONTROLS
D DIAGNOSTIC CIRCUITS
E DIMMING ILLUMINATION
CIRCUITS
F FUSED CIRCUITS
G MONITORING CIRCUITS
(GAUGES)
H OPEN
I NOT USED
J OPEN
K POWERTRAIN CONTROL
MODULE
L EXTERIOR LIGHTING
M INTERIOR LIGHTING
N NOT USED
O NOT USED
P POWER OPTION (BATTERY
FEED)
Q POWER OPTIONS (IGNITION
FEED)
R PASSIVE RESTRAINT
S SUSPENSION/STEERING
T TRANSMISSION/TRANSAXLE/
TRANSFER CASE
U OPEN
V SPEED CONTROL, WIPER/
WASHER
W OPEN
X AUDIO SYSTEMS
Y OPEN
Z GROUNDS
DESCRIPTION - SECTION IDENTIFICATION AND
INFORMATION
The wiring diagrams are grouped into individual
sections. If a component is most likely found in a par-
ticular group, it will be shown complete (all wires,
connectors, and pins) within that group. For exam-
ple, the Auto Shutdown Relay is most likely to be
found in Group 30, so it is shown there complete. It
can, however, be shown partially in another group if
it contains some associated wiring.
Splice diagrams in Section 8W-70 show the entire
splice and provide references to other sections the
splices serves. Section 8W-70 only contains splice dia-
grams that are not shown in their entirety some-
where else in the wiring diagrams.
Section 8W-80 shows each connector and the cir-
cuits involved with that connector. The connectors
are identified using the name/number on the dia-
gram pages.
WIRING SECTION CHART
GROUP TOPIC
8W-01 thru
8W-09General information and Diagram
Overview
8W-10 thru
8W-19Main Sources of Power and
Vehicle Grounding
8W-20 thru
8W-29Starting and Charging
8W-30 thru
8W-39Powertrain/Drivetrain Systems
8W-40 thru
8W-49Body Electrical items and A/C
8W-50 thru
8W-59Exterior Lighting, Wipers and
Trailer Tow
8W-60 thru
8W-69Power Accessories
8W-70 Splice Information
8W-80 Connector Pin Outs
8W-91 Connector, Ground and Splice
Locations
8W - 01 - 6 8W-01 WIRING DIAGRAM INFORMATIONDR
WIRING DIAGRAM INFORMATION (Continued)

Component Page
Manifold Absolute Pressure Sensor........ 8W-30
Mode Door Actuators................... 8W-42
Multi-Function Switch............ 8W-40, 52, 53
Natural Vacuum Leak Detection Assembly . . 8W-30
Output Speed Sensor................... 8W-31
Overhead Map/Reading Lamp......... 8W-44, 49
Oxygen Sensor Downstream Relay........ 8W-30
Oxygen Sensors....................... 8W-30
Park Brake Switch.................... 8W-40
Park Lamp Relay................... 8W-50, 52
Park/Turn Signal Lamps............. 8W-50, 52
Power Mirrors........................ 8W-62
Power Outlets........................ 8W-41
Power Seat Motors.................... 8W-63
Power Seat Switches................... 8W-63
Power Steering Pressure Switch.......... 8W-30
Power Window Circuit Breaker........... 8W-10
Power Window Motors.................. 8W-60
Power Window Switches................ 8W-60
Powertrain Control Module.............. 8W-30
PTCS............................... 8W-10
PTO Switch.......................... 8W-30
Radio............................... 8W-47
Rear Window Defogger Relay............ 8W-48
Recirculation Door Actuator............. 8W-42
Remote Radio Switches................. 8W-47
Seat Belt Pretensioners................. 8W-43
Seat Belt Switch-Driver................ 8W-40
Seat Belt Tensioner Reducer............. 8W-40
Seat Heater Interface Module............ 8W-63
Sentry Key Immobilizer Module.......... 8W-39
Side Impact Sensors................... 8W-43
Speakers............................ 8W-47Component Page
Speed Control Servo................... 8W-33
Speed Control Switches................. 8W-33
Splices.............................. 8W-70
Starter Motor........................ 8W-21
Starter Motor Relay................... 8W-21
Tail/Stop Lamp....................... 8W-52
Tail/Stop/Turn Signal Lamps.......... 8W-51, 52
Tail/Turn Lamp....................... 8W-52
Tailgate Lamp........................ 8W-51
Throttle Position Sensor................ 8W-30
Tow/Haul Overdrive Switch........... 8W-30, 31
Trailer Tow Connectors................. 8W-54
Trailer Tow Relays.................... 8W-54
Transfer Case Control Module............ 8W-31
Transfer Case Mode Sensor.............. 8W-31
Transfer Case Selector Switch............ 8W-31
Transfer Case Shift Motor............... 8W-31
Transmission Control Relay............. 8W-31
Transmission Range Sensor.............. 8W-31
Transmission Solenoid Assembly.......... 8W-31
Transmission Solenoid/TRS Assembly...... 8W-31
Underhood Lamp...................... 8W-44
Vacuum Pump........................ 8W-30
Vistronic Fan Drive................. 8W-30, 70
Washer Fluid Level Switch.............. 8W-53
Washer Pump Motor-Front.............. 8W-53
Water In Fuel Sensor.................. 8W-30
Wheel Speed Sensors................... 8W-35
Wiper High/Low Relay................. 8W-53
Wiper Motor-Front.................... 8W-53
Wiper On/Off Relay.................... 8W-53
8W - 02 - 2 8W-02 COMPONENT INDEXDR