fuse DODGE RAM 1500 1998 2.G Repair Manual

OPERATION
The voltage gauge gives an indication to the vehi-
cle operator of the electrical system voltage. This
gauge is controlled by the instrument cluster circuit
board based upon cluster programming and elec-
tronic messages received by the cluster from the
Powertrain Control Module (PCM) on vehicles
equipped with a gasoline engine, or from the Engine
Control Module (ECM) on vehicles equipped with a
diesel engine over the Programmable Communica-
tions Interface (PCI) data bus. The voltage gauge is
an air core magnetic unit that receives battery cur-
rent on the instrument cluster electronic circuit
board through the fused ignition switch output (run-
start) circuit whenever the ignition switch is in the
On or Start positions. The cluster is programmed to
move the gauge needle back to the left end of the
scale after the ignition switch is turned to the Off
position. The instrument cluster circuitry controls
the gauge needle position and provides the following
features:
²System Voltage Message- Each time the clus-
ter receives a system voltage message from the PCM
or ECM indicating the system voltage is between
about 9.5 volts and about 15 volts, the gauge needle
is moved to the relative voltage position on the gauge
scale.
²System Voltage Low (Charge Fail) Message
- Each time the cluster receives three consecutive
messages from the PCM or ECM indicating the elec-
trical system voltage is less than about 9 volts
(charge fail condition), the gauge needle is moved to
the graduation on the far left end of the gauge scale
and the check gauges indicator is illuminated. The
gauge needle remains at the far left end of the gauge
scale and the check gauges indicator remains illumi-
nated until the cluster receives a single message
from the PCM or ECM indicating the electrical sys-
tem voltage is greater than about 9.5 volts (but less
than about 15.5 volts), or until the ignition switch is
turned to the Off position, whichever occurs first. On
vehicles equipped with the optional diesel engine, the
ECM is programmed to restrict the voltage gauge
needle to a position above the graduation on the far
left end of the gauge scale and suppress the check
engine indicator operation until after the engine
intake manifold air heater has completed a pre-heat
or post-heat cycle.²System Voltage High Message- Each time
the cluster receives three consecutive messages from
the PCM or ECM indicating the electrical system
voltage is greater than about 15.5 volts, the gauge
needle is moved to the graduation on the far right
end of the gauge scale and the check gauges indica-
tor is illuminated. The gauge needle remains at the
right end of the gauge scale and the check gauges
indicator remains illuminated until the cluster
receives a message from the PCM or ECM indicating
the electrical system voltage is less than about 15.0
volts (but greater than about 9.5 volts), or until the
ignition switch is turned to the Off position, which-
ever occurs first.
²Communication Error- If the cluster fails to
receive a system voltage message, it will hold the
gauge needle at the last indication for about five sec-
onds or until the ignition switch is turned to the Off
position, whichever occurs first. After five seconds,
the cluster will move the gauge needle to the far left
end of the gauge scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the voltage gauge needle
will be swept to several calibration points on the
gauge scale in a prescribed sequence in order to con-
firm the functionality of the gauge and the cluster
control circuitry.
On vehicles with a gasoline engine, the PCM con-
tinually monitors the system voltage to control the
generator output. On vehicles with a diesel engine,
the ECM continually monitors the system voltage to
control the generator output. The PCM or ECM then
sends the proper system voltage messages to the
instrument cluster. For further diagnosis of the volt-
age gauge or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). If the instrument cluster turns on the check
gauges indicator due to a charge fail or voltage high
condition, it may indicate that the charging system
requires service. For proper diagnosis of the charging
system, the PCM, the ECM, the PCI data bus, or the
electronic message inputs to the instrument cluster
that control the voltage gauge, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
DRINSTRUMENT CLUSTER 8J - 43
VOLTAGE GAUGE (Continued)

WAIT-TO-START INDICATOR
DESCRIPTION
A wait-to-start indicator is only found in the
instrument clusters for vehicles equipped with an
optional diesel engine (Fig. 35). The wait-to-start
indicator is located near the lower edge of the instru-
ment cluster, between the tachometer and the speed-
ometer. The wait-to-start indicator consists of stencil-
like cutout of the International Control and Display
Symbol icon for ªDiesel Preheatº in the opaque layer
of the instrument cluster overlay. The dark outer
layer of the overlay prevents the indicator from being
clearly visible when it is not illuminated. An amber
Light Emitting Diode (LED) behind the cutout in the
opaque layer of the overlay causes the icon to appear
in amber through the translucent outer layer of the
overlay when the indicator is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The wait-
to-start indicator is serviced as a unit with the
instrument cluster.
OPERATION
The wait-to-start indicator gives an indication to
the vehicle operator when the air temperature within
the diesel engine intake manifold is too cool for effi-
cient and reliable engine starting, and that the
intake air heater grids are energized in their pre-
heat operating mode. This indicator is controlled by a
transistor on the instrument cluster circuit board
based upon cluster programming and electronic mes-
sages received by the cluster from the Engine Control
Module (ECM) over the Programmable Communica-
tions Interface (PCI) data bus. The wait-to-start indi-
cator Light Emitting Diode (LED) is completely
controlled by the instrument cluster logic circuit, and
that logic will only allow this indicator to operate
when the instrument cluster receives a battery cur-
rent input on the fused ignition switch output (run-
start) circuit. Therefore, the LED will always be off
when the ignition switch is in any position except On
or Start. The LED only illuminates when it is pro-
vided a path to ground by the instrument cluster
transistor. The instrument cluster will turn on the
wait-to-start indicator for the following reasons:
²Wait-To-Start Lamp-On Message- Each time
the cluster receives a wait-to-start lamp-on message
from the ECM indicating that the air temperature
within the intake manifold is too cool for efficient
and reliable engine starting, the wait-to-start indica-
tor will be illuminated. The indicator remains illumi-nated until the cluster receives a wait-to-start lamp-
off message, until the ECM detects that the engine is
running or until the ignition switch is turned to the
Off position, whichever occurs first.
²Actuator Test- Each time the cluster is put
through the actuator test, the wait-to-start indicator
will be turned on, then off again during the bulb
check portion of the test to confirm the functionality
of the LED and the cluster control circuitry.
The ECM continually monitors the engine intake
air temperature sensor to determine when the intake
air heater grids should be energized in their pre-heat
operating mode. The ECM then sends the proper
wait-to-start lamp-on and lamp-off messages to the
instrument cluster. For further diagnosis of the wait-
to-start indicator or the instrument cluster circuitry
that controls the indicator, (Refer to 8 - ELECTRI-
CAL/INSTRUMENT CLUSTER - DIAGNOSIS AND
TESTING). For proper diagnosis of the engine intake
air temperature sensor, the intake air heater grid
control circuits, the ECM, the PCI data bus, or the
electronic message inputs to the instrument cluster
that control the wait-to-start indicator, a DRBIIIt
scan tool is required. Refer to the appropriate diag-
nostic information.
WASHER FLUID INDICATOR
DESCRIPTION
A washer fluid indicator is standard equipment on
all instrument clusters. The washer fluid indicator
consists of the words ªLOW WASHº, which appear in
the lower portion of the odometer/trip odometer Vac-
uum-Fluorescent Display (VFD) unit (Fig. 36). The
VFD is soldered onto the cluster electronic circuit
board and is visible through a window with a smoked
clear lens located on the lower edge of the tachome-
ter gauge dial face of the cluster overlay. The dark
lens over the VFD prevents the indicator from being
clearly visible when it is not illuminated. The ªLOW
WASHº text appears in an amber color and at the
same lighting level as the odometer/trip odometer
information when it is illuminated by the instrument
cluster electronic circuit board. The washer fluid
indicator is serviced as a unit with the VFD in the
instrument cluster.
OPERATION
The washer fluid indicator gives an indication to
the vehicle operator that the fluid level in the washer
Fig. 35 Wait-To-Start Indicator
Fig. 36 Washer Fluid Indicator
8J - 44 INSTRUMENT CLUSTERDR

reservoir is low. This indicator is controlled by the
instrument cluster circuit board based upon cluster
programming and electronic messages received by
the cluster from the Front Control Module (FCM)
over the Programmable Communications Interface
(PCI) data bus. The washer fluid indicator is com-
pletely controlled by the instrument cluster logic cir-
cuit, and that logic will only allow this indicator to
operate when the instrument cluster receives a bat-
tery current input on the fused ignition switch out-
put (run-start) circuit. Therefore, the indicator will
always be off when the ignition switch is in any posi-
tion except On or Start. The indicator only illumi-
nates when it is switched to ground by the
instrument cluster circuitry. The instrument cluster
will turn on the washer fluid indicator for the follow-
ing reasons:
²Washer Fluid Indicator Lamp-On Message-
Each time the cluster receives a washer fluid indica-
tor lamp-on message from the FCM indicating that a
low washer condition has been detected for sixty con-
secutive seconds, the washer fluid indicator is illumi-
nated and a single chime tone is sounded. The
indicator remains illuminated until the cluster
receives a washer fluid indicator lamp-off message
for sixty consecutive seconds from the FCM or until
the ignition switch is turned to the Off position,
whichever occurs first. The chime tone feature will
only repeat during the same ignition cycle if the
washer fluid indicator is cycled off and then on again
by the appropriate washer fluid lamp messages from
the FCM.
²Actuator Test- Each time the cluster is put
through the actuator test, the washer fluid indicator
will be turned on, then off again during the VFD por-
tion of the test to confirm the functionality of the
VFD and the cluster control circuitry.
The FCM continually monitors the washer fluid
level switch in the washer reservoir to determine the
level of the washer fluid. The FCM then sends the
proper washer fluid indicator lamp-on and lamp-off
messages to the instrument cluster. For further diag-
nosis of the washer fluid indicator or the instrument
cluster circuitry that controls the indicator, (Refer to
8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAG-
NOSIS AND TESTING). For proper diagnosis of the
washer fluid level switch, the FCM, the PCI data
bus, or the electronic message inputs to the instru-
ment cluster that control the washer fluid indicator,
a DRBIIItscan tool is required. Refer to the appro-
priate diagnostic information.WATER-IN-FUEL INDICATOR
DESCRIPTION
A water-in-fuel indicator is only found in the
instrument clusters for vehicles equipped with an
optional diesel engine (Fig. 37). The water-in-fuel
indicator is located near the lower edge of the instru-
ment cluster, between the tachometer and the speed-
ometer. The water-in-fuel indicator consists of stencil-
like cutout of the International Control and Display
Symbol icon for ªWater In Fuelº in the opaque layer
of the instrument cluster overlay. The dark outer
layer of the overlay prevents the indicator from being
clearly visible when it is not illuminated. A red Light
Emitting Diode (LED) behind the cutout in the
opaque layer of the overlay causes the icon to appear
in red through the translucent outer layer of the
overlay when the indicator is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The
water-in-fuel indicator is serviced as a unit with the
instrument cluster.
OPERATION
The water-in-fuel indicator gives an indication to
the vehicle operator when there is excessive water in
the fuel system. This indicator is controlled by a
transistor on the instrument cluster circuit board
based upon the cluster programming and electronic
messages received by the cluster from the Engine
Control Module (ECM) over the Programmable Com-
munications Interface (PCI) data bus. The water-in-
fuel indicator Light Emitting Diode (LED) is
completely controlled by the instrument cluster logic
circuit, and that logic will only allow this indicator to
operate when the instrument cluster receives a bat-
tery current input on the fused ignition switch out-
put (run-start) circuit. Therefore, the LED will
always be off when the ignition switch is in any posi-
tion except On or Start. The LED only illuminates
when it is provided a path to ground by the instru-
ment cluster transistor. The instrument cluster will
turn on the water-in-fuel indicator for the following
reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the water-in-fuel indicator
is illuminated for about two seconds as a bulb test.
²Water-In-Fuel Lamp-On Message- Each time
the cluster receives a water-in-fuel lamp-on message
from the ECM indicating that there is excessive
Fig. 37 Water-In-Fuel Indicator
DRINSTRUMENT CLUSTER 8J - 45
WASHER FLUID INDICATOR (Continued)

Instrument Cluster transmits a message via J1850
informing the the FCM. The FCM will then turn off
the headlamps, park lamps and fog lamps. This fea-
ture (load shed) prevents the vehicle battery from
being discharged when the vehicle lights have been
left ON.
HEADLAMP TIME DELAY SYSTEM
The headlamp time delay system is activated by
turning the headlamps ON (high or low beam) while
the engine is running, turning the ignition switch
OFF, and then turning the headlamp switch OFF
within 45 seconds. The system will not activate if
more than 45 seconds elapse between ignition switch
OFF and headlamp switch OFF. The FCM will allow
the headlamps to remain ON for 60 seconds (config-
urable) before they automatically turn off (If the key
is in the ignition during the headlamp time delay
mode, then the headlamps including panel dimming
will be ON).
LAMP OUTAGE
If one or more of the following lamps (Low and/or
High beams, Brake and/or Turn Signal) are out, then
a ªlamps outº indicator located in the cluster will
illuminate.
OPTICAL HORN/HIGH BEAMS
When the multiplexed multifunction switch is
pulled to the first detent (optical horn) signal, the
headlamps are ON, the Instrument Cluster shall
send a message via J1850 to the FCM to turn on the
headlamps drivers to illuminate all four filaments
(Low and High beams). When the multifunction
switch is pulled to the second detent (high beam) sig-
nal and the headlamps are ON, the Instrument Clus-
ter shall send a message via J1850 to the FCM to
turn on the headlamps drivers. The High Beams are
illuminated and the Low Beams and Fog Lamps (if
ON) are extinguished. If the headlamps were in the
high beam configuration when power was removedfrom the headlamps, the headlamps will return to
their last state prior to being shut off.
DIAGNOSIS AND TESTING - LAMPS/LIGHTING
- EXTERIOR
WARNING: EYE PROTECTION SHOULD BE USED
WHEN SERVICING GLASS COMPONENTS. PER-
SONAL INJURY CAN RESULT.
CAUTION: Do not touch the glass of halogen bulbs
with fingers or other possibly oily surface, reduced
bulb life will result. Do not use bulbs other than
those indicated in the Bulb Application table. Dam-
age to lamp and/or Daytime Running Lamp Module
can result. Do not use fuses, circuit breakers or
relays having greater amperage value than indi-
cated on the fuse panel or in the Owners Manual.
When a vehicle experiences problems with the
headlamp system, verify the condition of the battery
connections, fuses, charging system, headlamp bulbs,
wire connectors, relay, multifunction switch, and
headlamp switch. Refer to the appropriate wiring
information.
Each vehicle is equipped with various lamp assem-
blies. A good ground is necessary for proper lighting
operation. Grounding is provided by the lamp socket
when it comes in contact with the metal body, or
through a separate ground wire.
When changing lamp bulbs check the socket for
loose pin connections and corrosion. Repair as neces-
sary.
When it is necessary to remove components to ser-
vice another, it should not be necessary to apply
excessive force or bend a component to remove it.
Before damaging a trim component, verify hidden
fasteners or captured edges are not holding the com-
ponent in place.
DRLAMPS/LIGHTING - EXTERIOR 8L - 3
LAMPS/LIGHTING - EXTERIOR (Continued)

CONDITION POSSIBLE CAUSES CORRECTION
FOG LAMPS ARE DIM
WITH ENGINE
RUNNING ABOVE IDLE1. Charging system output too low. 1. Test and repair charging system. Refer to
Electrical, Charging.
2. Poor lighting circuit ground. 2. Test for voltage drop across ground
locations. Refer to Electrical, Wiring
Information.
3. High resistance in fog lamp
circuit.3. Test amperage draw of fog lamp circuit.
FOG LAMPS FLASH
RANDOMLY1. Poor lighting circuit ground. 1. Test for voltage drop across ground
locations. Refer to Electrical, Wiring
Information.
2. Variable resistance in fog lamp
circuit.2. Test amperage draw of fog lamp circuit.
3. Faulty fog lamp switch (part of
headlamp switch).3. Replace headlamp switch.
4. Loose or corroded terminals or
splices in circuit.4. Inspect and repair all connectors and splices.
Refer to Electrical, Wiring Information.
5. Is relay engaging properly? 5. Verify function of fog lamp relay in IPM.
6. J1850 Bus Communication. 6. Verify J1850 message (fog lamp info)
transmitted from Instrument Cluster and
received by FCM.
FOG LAMPS DO NOT
ILLUMINATE1. Blown fuse for fog lamp. 1. Replace fuse. Refer to Electrical, Wiring
Information.
2. No ground at fog lamps. 2. Repair circuit ground. Refer to Electrical,
Wiring Information.
3. Faulty fog lamp switch (part of
headlamp switch).3. Replace headlamp switch.
4. Broken connector terminal or
wire splice in fog lamp circuit.4. Repair connector terminal or wire splice.
5. Faulty or burned out bulb. 5. Replace bulb.
6. Is relay engaging? 6. Verify function of fog lamp relay in IPM.
7. J1850 Bus Communication. 7. Verify J1850 message (fog lamp info)
transmitted from Instrument Cluster and
received by FCM.
DAYTIME RUNNING LAMP (CANADA ONLY) DIAGNOSIS
CONDITION POSSIBLE CAUSES CORRECTION
DAYTIME RUNNING
LAMPS DO NOT
OPERATE1. Parking brake engaged. 1. Disengage parking brake.
2. Parking brake circuit shorted
to ground.2. Check cluster telltale, refer to the appropriate
wiring information.
3. Headlamp circuit shorted to
ground.3. Refer to the appropriate wiring information.
4. FCM, Instrument Cluster not
programed with Canadian
country code.4. Check country code.
8L - 6 LAMPS/LIGHTING - EXTERIORDR
LAMPS/LIGHTING - EXTERIOR (Continued)

STANDARD PROCEDURE
SAFETY PRECAUTIONS
WARNING: EYE PROTECTION SHOULD BE USED
WHEN SERVICING GLASS COMPONENTS. PER-
SONAL INJURY CAN RESULT.
CAUTION: Do not touch the glass of halogen bulbs
with fingers or other possibly oily surface, reduced
bulb life will result.Do not use bulbs with higher
candle power than indicated in the Bulb Application
table . Damage to lamp and/or Daytime Running
Lamp Module can result.Do not use fuses, circuit
breakers or relays having greater amperage value
than indicated on the fuse panel or in the Owners
Manual.
When it is necessary to remove components to ser-
vice another, it should not be necessary to apply
excessive force or bend a component to remove it.
Before damaging a trim component, verify hidden
fasteners or captured edges are not holding the com-
ponent in place.
SPECIFICATIONS
EXTERIOR LAMPS
CAUTION: Do not use bulbs that have a higher can-
dle power than the bulb listed in the Bulb Applica-
tion Table. Damage to lamp can result. Do not touch
halogen bulbs with fingers or other oily surfaces.
Bulb life will be reduced.
The following Bulb Application Table lists the lamp
title on the left side of the column and trade number
or part number on the right.
BULB APPLICATION TABLE
LAMP BULB
Backup - w/cargo box 3057
Backup - w/box off 1156
Center High Mounted
Stop lamp912
Fog lamp 9006LL
Front Park/Turn Signal 3157NA
Head lamp 9007
License Plate 168
Tail, Brake, Turn Signal -
w/cargo box3057
LAMP BULB
Tail, Brake, Turn Signal -
w/box off1157
Side Marker, Tail Gate,
Cab Clearance168
BACKUP LAMP
REMOVAL
REMOVAL - WITH CARGO BOX
(1) Remove and isolate the negative battery cable.
(2) Remove the taillamp 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 backup lamp 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. 1).
(3) Separate the tail lamp lens from the tail lamp
housing.
(4) Push the backup lamp bulb inward and rotate
it counter-clockwise.
(5) Remove the backup lamp bulb from the backup
lamp socket.
INSTALLATION
INSTALLATION - WITH CARGO BOX
(1) Install the backup lamp bulb into the lamp
back plate.
Fig. 1 Tail Lamp Lens
DRLAMPS/LIGHTING - EXTERIOR 8L - 7
LAMPS/LIGHTING - EXTERIOR (Continued)

(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 backup lamp bulb into the backup
lamp socket by pushing inward and rotating it clock-
wise.
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.
BACKUP LAMP SWITCH
DESCRIPTION
Vehicles equipped with a manual transmission
have a normally open, spring-loaded plunger typeback-up lamp switch (Fig. 2). The backup lamp
switch is located in a threaded hole on the side of the
manual transmission housing. The backup lamp
switch has a threaded body and a hex formation near
the plunger end of the switch, and an integral con-
nector at the opposite end of the switch. When
installed, only the connector and the hex formation
are visible on the outside of the transmission hous-
ing. Vehicles with an optional electronic automatic
transmission have a Transmission Range Sensor
(TRS) that is used to perform several functions,
including that of the backup lamp switch. The TRS is
described in further detail elsewhere in this service
information. The backup lamp switch cannot be
adjusted or repaired and, if faulty or damaged, the
entire switch unit must be replaced.
OPERATION
The backup lamp switch controls the flow of bat-
tery voltage to the backup lamp bulbs through an
output on the back-up lamp feed circuit. The switch
plunger is mechanically actuated by the gearshift
mechanism within the transmission, which will
depress the switch plunger and close the switch con-
tacts whenever the reverse gear has been selected.
The switch receives battery voltage through a fuse in
the Integrated Power Module (IPM) on a fused igni-
tion switch output (run) circuit whenever the ignition
switch is in the On position. A take out of the engine
wire harness connects the backup lamp switch to the
vehicle electrical system. The backup lamp switch
and circuits can be tested using conventional diag-
nostic tools and methods.
DIAGNOSIS AND TESTING - BACKUP LAMP
SWITCH
(1) Disconnect and isolate the battery negative
cable.
(2) Raise and support the vehicle.
(3) Locate and disconnect the engine wire harness
connector for the backup lamp switch.
(4) Check for continuity between the two terminal
pins in the backup lamp switch connector.
(a) With the gear selector lever in the Reverse
position, there should be continuity.
(b) With the gear selector lever in any position
other than Reverse, there should be no continuity.
Fig. 2 Backup Lamp Switch - Typical
1 - MANUAL TRANSMISSION
2 - BACKUP LAMP SWITCH
3 - ENGINE WIRE HARNESS
8L - 8 LAMPS/LIGHTING - EXTERIORDR
BACKUP LAMP (Continued)

ment of the vehicle. The front fog lamp relay is a
conventional International Standards Organization
(ISO) micro relay (Fig. 9). Relays conforming to the
ISO specifications have common physical dimensions,
current capacities, terminal patterns, and terminal
functions. The relay is contained within a small, rect-
angular, molded plastic housing and is connected to
all of the required inputs and outputs by five integral
male spade-type terminals that extend from the bot-
tom of the relay base.
The front fog lamp relay cannot be adjusted or
repaired and, if faulty or damaged, the unit must be
replaced.
OPERATION
The front fog lamp relay is an electromechanical
switch that uses a low current input from the Front
Control Module (FCM) to control a high current out-
put to the front fog lamps. The movable common feed
contact point is held against the fixed normally
closed contact point by spring pressure. When the
relay coil is energized, an electromagnetic field is
produced by the coil windings. This electromagnetic
field draws the movable relay contact point away
from the fixed normally closed contact point, and
holds it against the fixed normally open contact
point. When the relay coil is de-energized, spring
pressure returns the movable contact point back
against the fixed normally closed contact point. A
resistor is connected in parallel with the relay coil in
the relay, and helps to dissipate voltage spikes and
electromagnetic interference that can be generated as
the electromagnetic field of the relay coil collapses.
The front fog lamp relay terminals are connected
to the vehicle electrical system through a connector
receptacle in the Power Distribution Center (PDC).
The inputs and outputs of the front fog lamp relay
include:
²Common Feed Terminal- The common feed
terminal (30) receives battery voltage at all times
from a fuse in the PDC through a fused B(+) circuit.
²Coil Ground Terminal- The coil ground termi-
nal (85) is connected to a control output of the Front
Control Module (FCM) through a front fog lamp relay
control circuit. The FCM controls front fog lamp oper-
ation by controlling a ground path through this cir-
cuit.
²Coil Battery Terminal- The coil battery ter-
minal (86) receives battery voltage at all times from
a fuse in the PDC through a fused B(+) circuit.
²Normally Open Terminal- The normally open
terminal (87) is connected to the front fog lamps
through a front fog lamp relay output circuit and
provides battery voltage to the front fog lamps when-
ever the relay is energized.²Normally Closed Terminal- The normally
closed terminal (87A) is not connected in this appli-
cation.
The front fog lamp relay can be diagnosed using
conventional diagnostic tools and methods. Refer to
the appropriate wiring information for diagnosis and
testing of the front fog lamp micro-relay and for com-
plete wiring diagrams.
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SEAT BELT TENSIONER,
FRONT IMPACT SENSORS, SIDE CURTAIN AIRBAG,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-
TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER DIAGNOSIS OR SERVICE. THIS IS THE ONLY
SURE WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the cover for the Power Distribution
Center (PDC).
(3) Remove the front fog lamp relay by grasping it
firmly and pulling it straight out from the receptacle
in the PDC.
INSTALLATION
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SEAT BELT TENSIONER,
FRONT IMPACT SENSORS, SIDE CURTAIN AIRBAG,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-
TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER DIAGNOSIS OR SERVICE. THIS IS THE ONLY
SURE WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
DRLAMPS/LIGHTING - EXTERIOR 8L - 13
FOG LAMP RELAY (Continued)

PARK LAMP RELAY
DESCRIPTION
The park lamp relay is located in the Power Dis-
tribution Center (PDC) of the vehicle. The park lamp
relay is a conventional International Standards
Organization (ISO) micro relay (Fig. 17). Relays con-
forming to the ISO specifications have common phys-
ical dimensions, current capacities, terminal
patterns, and terminal functions.
The park lamp relay cannot be adjusted or
repaired and, if faulty or damaged, the unit must be
replaced.
OPERATION
The park lamp relay is an electromechanical
switch that uses a low current input from the Front
Control Module (FCM) to control a high current out-
put to the park lamps. The movable common feed
contact point is held against the fixed normally
closed contact point by spring pressure. When the
relay coil is energized, an electromagnetic field is
produced by the coil windings. This electromagnetic
field draws the movable relay contact point away
from the fixed normally closed contact point, and
holds it against the fixed normally open contact
point. When the relay coil is de-energized, spring
pressure returns the movable contact point back
against the fixed normally closed contact point. A
resistor is connected in parallel with the relay coil in
the relay, and helps to dissipate voltage spikes and
electromagnetic interference that can be generated as
the electromagnetic field of the relay coil collapses.The park lamp relay terminals are connected to
the vehicle electrical system through a connector in
the Junction Block (JB). The inputs and outputs of
the headlamp low beam relay include:
²Common Feed Terminal- The common feed
terminal (30) is connected to the park lamps through
the park lamp relay output circuit and provides
ground to the park lamps when the relay is de-ener-
gized, and battery current to the park lamps when-
ever the relay is energized.
²Coil Ground Terminal- The coil ground termi-
nal (85) is connected to a control output of the Front
Control Module (FCM) through a park lamp relay
control circuit. The FCM controls park lamp opera-
tion by controlling a ground path through this cir-
cuit.
²Coil Battery Terminal- The coil battery ter-
minal (86) receives battery current at all times from
a fuse in the PDC through a fused B(+) circuit.
²Normally Open Terminal- The normally open
terminal (87) receives battery current at all times
from a fuse in the Power Distribution Center (PDC)
through a fused B(+) circuit.
²Normally Closed Terminal- The normally
closed terminal (87A) is connected to ground at all
times.
The park lamp relay can be diagnosed using con-
ventional diagnostic tools and methods.
DIAGNOSIS AND TESTING - PARK LAMP
RELAY
The park lamp relay (Fig. 18) is located in the
Power Distribution Center (PDC). Refer to the appro-
priate wiring information.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SEAT BELT TENSIONER,
FRONT IMPACT SENSORS, SIDE CURTAIN AIRBAG,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-
TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER DIAGNOSIS OR SERVICE. THIS IS THE ONLY
SURE WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
(1) Remove the park lamp relay from the PDC.
(2) A relay in the de-energized position should
have continuity between terminals 87A and 30, and
Fig. 17 ISO Micro Relay
30 - COMMON FEED
85 - COIL GROUND
86 - COIL BATTERY
87 - NORMALLY OPEN
87A - NORMALLY CLOSED
8L - 20 LAMPS/LIGHTING - EXTERIORDR

The compass unit also will compensate for magne-
tism the body of the vehicle may acquire during nor-
mal use. However, avoid placing anything magnetic
directly on the roof of the vehicle. Magnetic mounts
for an antenna, a repair order hat, or a funeral pro-
cession flag can exceed the compensating ability of
the compass unit if placed on the roof panel. Mag-
netic bit drivers used on the fasteners that hold the
overhead console assembly to the roof header can
also affect compass operation. If the vehicle roof
should become magnetized, the demagnetizing and
calibration procedures found in this section may be
required to restore proper compass operation.
TEMPERATURE DISPLAY
All the available overhead consoles on this model
include Temperature information. The temperature
displays the outside ambient temperature in whole
degrees. The temperature display can be toggled
from Fahrenheit to Celsius by selecting the desired
U.S./Metric option from the customer programmable
features. The displayed temperature is not an instant
reading of conditions, but an average temperature. It
may take the temperature display several minutes to
respond to a major temperature change, such as driv-
ing out of a heated garage into winter temperatures.
When the ignition switch is turned to the Off posi-
tion, the last displayed temperature reading stays in
the electronic control modules, (CMTC, EVIC) mem-
ory. When the ignition switch is turned to the On
position again, the electronic module will display the
memory temperature for one minute; then update the
display to the current average temperature reading
within five minutes.The temperature function is supported by an ambi-
ent temperature sensor. This sensor is mounted out-
side the passenger compartment near the front and
center of the vehicle, and is hard wired to the Front
Control Module (FCM). The FCM sends temperature
status messages to the module over the J1850 PCI
data bus circuit. For more information on the ambi-
ent temperature sensor, refer to Ambient Tempera-
ture Sensor later in this section.
Following are general descriptions of the major
components used in the overhead console. Refer to
Wiring Diagrams for complete circuit schematics.
OPERATION
Refer to the vehicle Owner's Manual for specific
operation of each overhead console and its systems.
DIAGNOSIS AND TESTING - OVERHEAD
CONSOLE
If the problem with the overhead console is an
inaccurate or scrambled display, refer toSELF-DI-
AGNOSTIC TESTlater in this text. If the problem
with the overhead console is incorrect Vacuum Fluo-
rescent Display (VFD) dimming levels, use a DRB
IIItscan tool and the proper Diagnostic Procedures
manual to test for the correct dimming message
inputs being received from the Body Control Module
(BCM) or Front Control Module (FCM) over the
J1850 Programmable Communications Interface
(PCI) data bus circuit. If the problem is a no-display
condition, use the following procedure. For complete
circuit diagrams, refer toOverhead Consolein the
Wiring Diagrams section of the service manual.
(1) Remove the overhead console from the head-
liner (Refer to 8 - ELECTRICAL/OVERHEAD CON-
SOLE - REMOVAL).
(2) Check for battery voltage at the overhead con-
sole electrical connector. Refer to Wiring for connec-
tor information. If OK, go to Step 3. If not OK, Check
for battery voltage at the appropriate B(+) fuse in the
integrated power module, repair the open fused B(+)
circuit as required.
(3) Turn the ignition switch to the On position.
Check the fused ignition switch output circuit(s) at
the overhead console electrical connector. If OK, go to
Step 4. If not OK, repair the open or shorted circuit
as required.
(4) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Check for continuity between the ground circuit cav-
ity of the overhead console electrical connector and a
good ground. There should be continuity. If OK, refer
toSELF-DIAGNOSTIC TESTbelow for further
diagnosis of the electronics module and the J1850
PCI data bus circuit. If not OK, repair the open
ground circuit as required.
Fig. 1 DR OVERHEAD CONSOLE ± EVIC
8M - 2 MESSAGE SYSTEMSDR
OVERHEAD CONSOLE (Continued)