2002 DODGE RAM PCM

remains illuminated until the cluster receives an
overdrive off lamp-off message from the PCM, 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 indicator will be
turned on during the bulb check portion of the test to
confirm the functionality of the LED and the cluster
control circuitry.
The PCM continually monitors the overdrive off
switch to determine the proper outputs to the auto-
matic transmission, then sends the proper messages
to the instrument cluster. For further diagnosis of
the overdrive off indicator or the instrument cluster
circuitry that controls the LED, (Refer to 8 - ELEC-
TRICAL/INSTRUMENT CLUSTER - DIAGNOSIS
AND TESTING). For proper diagnosis of the over-
drive control system, the PCM, the CCD data bus, or
the message inputs to the instrument cluster that
control the overdrive off indicator, a DRBIIItscan
tool is required. Refer to the appropriate diagnostic
information.
SEATBELT INDICATOR
DESCRIPTION
A seatbelt indicator is standard equipment on all
instrument clusters. The seatbelt indicator is located
near the lower edge of the instrument cluster overlay,
to the right of center. The seatbelt indicator consists
of a stencilled cutout of the International Control and
Display Symbol icon for ªSeat Beltº 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
lens 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 indi-
cator is illuminated from behind by a Light Emitting
Diode (LED) soldered onto the instrument cluster
electronic circuit board. The seatbelt indicator is ser-
viced as a unit with the instrument cluster.
OPERATION
The seatbelt indicator gives an indication to the
vehicle operator of the status of the driver side front
seatbelt buckle. This indicator is controlled by a tran-
sistor on the instrument cluster circuit board based
upon the cluster programming, and a hard wired
input from the seatbelt switch in the driver side front
seatbelt through the seat belt switch sense circuit.
The seatbelt indicator Light Emitting Diode (LED)
receives battery current on the instrument cluster
electronic circuit board through the fused ignition
switch output (st-run) circuit whenever the ignitionswitch is in the On or Start positions; therefore, the
indicator will always be off when the ignition switch
is in any position except On or Start. The LED only
illuminates when it is switched to ground by the
instrument cluster transistor. The instrument cluster
will turn on the seatbelt indicator for the following
reasons:
²Seatbelt Reminder Function- Each time the
cluster receives a battery current input on the fused
ignition switch output (st-run) circuit, the indicator
will be illuminated as a seatbelt reminder for about
seven seconds, or until the ignition switch is turned
to the Off position, whichever occurs first. This
reminder function will occur regardless of the status
of the seatbelt switch input to the cluster.
²Driver Side Front Seatbelt Not Buckled-
Following the seatbelt reminder function, each time
the cluster receives a ground input on the seat belt
switch sense circuit (seatbelt switch closed - seatbelt
unbuckled) with the ignition switch in the Start or
On positions, the indicator will be illuminated. The
seatbelt indicator remains illuminated until the seat
belt switch sense input to the cluster is an open cir-
cuit (seatbelt switch opened - seatbelt buckled), 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 indicator will be
turned on during the bulb check portion of the test to
confirm the functionality of the LED and the cluster
control circuitry.
The seatbelt switch input to the instrument cluster
circuitry can be diagnosed using conventional diag-
nostic tools and methods. For further diagnosis of the
seatbelt indicator or the instrument cluster circuitry
that controls the LED, (Refer to 8 - ELECTRICAL/
INSTRUMENT CLUSTER - DIAGNOSIS AND
TESTING).
SERVICE REMINDER
INDICATOR
DESCRIPTION
A Service Reminder Indicator (SRI) is standard
equipment on all instrument clusters. However, on
vehicles not equipped with certain optional heavy
duty emission cycle gasoline engines, this indicator is
electronically disabled. The SRI is located near the
lower edge of the instrument cluster overlay, to the
left of center. The SRI consists of a stencilled cutout
of the words ªMAINT REQDº 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
lens behind the cutout in the opaque layer of the
BR/BEINSTRUMENT CLUSTER 8J - 27
OVERDRIVE OFF INDICATOR (Continued)

overlay causes the ªMAINT REQDº text to appear in
amber through the translucent outer layer of the
overlay when the indicator is illuminated from
behind by a Light Emitting Diode (LED) soldered
onto the instrument cluster electronic circuit board.
The SRI is serviced as a unit with the instrument
cluster.
OPERATION
The Service Reminder Indicator (SRI) gives an
indication to the vehicle operator when engine emis-
sions maintenance procedures should be performed.
This indicator is controlled by a transistor on the
instrument cluster circuit board based upon the clus-
ter programming and electronic messages received by
the cluster from the Powertrain Control Module
(PCM) over the Chrysler Collision Detection (CCD)
data bus. The SRI Light Emitting Diode (LED)
receives battery current on the instrument cluster
electronic circuit board through the fused ignition
switch output (st-run) circuit whenever the ignition
switch is in the On or Start positions; therefore, the
LED will always be off when the ignition switch is in
any position except On or Start. The LED only illu-
minates when it is provided a path to ground by the
instrument cluster transistor. The instrument cluster
will turn on the SRI for the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the SRI is illuminated for
about two seconds as a bulb test.
²Service Required Lamp-On Message- Each
time the cluster receives a service required lamp-on
message from the PCM indicating that an emissions
maintenance interval has been reached, the SRI will
be illuminated. The indicator remains illuminated
until the cluster receives a service required lamp-off
message from the PCM, 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 SRI will be turned on
during the bulb check portion of the test to confirm
the functionality of the LED and the cluster control
circuitry.
The PCM continually monitors the vehicle speed
sensor to determine the distance the vehicle has been
driven, then sends the proper messages to the instru-
ment cluster. Once the SRI has been illuminated and
the required emissions maintenance procedures have
been completed, the PCM must be reset using a
DRBIIItscan tool before it will send the proper ser-
vice required lamp-off message to the instrument
cluster. Refer to the appropriate diagnostic informa-
tion. For further diagnosis of the SRI or the instru-
ment cluster circuitry that controls the LED, (Refer
to 8 - ELECTRICAL/INSTRUMENT CLUSTER -
DIAGNOSIS AND TESTING). For proper diagnosisof the PCM, the CCD data bus, or the message
inputs to the instrument cluster that control the SRI,
a DRBIIItscan tool is required. Refer to the appro-
priate diagnostic information.
SHIFT INDICATOR (TRANSFER
CASE)
DESCRIPTION
A four-wheel drive indicator is standard equipment
on all instrument clusters. However, on vehicles not
equipped with the optional four-wheel drive system,
this indicator is mechanically disabled. The four-
wheel drive indicator is located near the lower edge
of the instrument cluster overlay, to the right of cen-
ter. The four-wheel drive indicator consists of a sten-
cilled cutout of the text ª4WDº 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
lens behind the cutout in the opaque layer of the
overlay causes the ª4WDº text to appear in amber
through the translucent outer layer of the overlay
when the indicator is illuminated from behind by a
Light Emitting Diode (LED) soldered onto the instru-
ment cluster electronic circuit board. The four-wheel
drive indicator is serviced as a unit with the instru-
ment cluster.
OPERATION
The four-wheel drive indicator lamp gives an indi-
cation to the vehicle operator that a four-wheel drive
operating mode is engaged. The indicator will be illu-
minated when either high range (4H) or low range
(4L) have been selected with the transfer case shift
lever. This indicator is controlled by a transistor on
the instrument cluster circuit board based upon the
cluster programming, and a hard wired input from
the four-wheel drive switch on the front axle discon-
nect housing. The four-wheel drive indicator Light
Emitting Diode (LED) receives battery current on the
instrument cluster electronic circuit board through
the fused ignition switch output (st-run) circuit
whenever the ignition switch is in the On or Start
positions; therefore, the lamp will always be off when
the ignition switch is in any position except On or
Start. The LED only illuminates when it is switched
to ground by the instrument cluster transistor.
The four-wheel drive switch is connected in series
between ground and the four-wheel drive switch
sense input to the instrument cluster. For further
information on the transfer case and the transfer
case operating ranges, (Refer to 21 - TRANSMIS-
SION/TRANSAXLE/TRANSFER CASE - OPERA-
TION. For further information on the front axle
8J - 28 INSTRUMENT CLUSTERBR/BE
SERVICE REMINDER INDICATOR (Continued)

illumination lighting with the exterior lamps turned
On, the white graphics appear blue-green, while the
red graphics still appear red. The orange gauge nee-
dle is internally illuminated. Gauge illumination is
provided by replaceable incandescent bulb and bulb
holder units located on the instrument cluster elec-
tronic circuit board. The speedometer is serviced as a
unit with the instrument cluster.
OPERATION
The speedometer gives an indication to the vehicle
operator of the vehicle road speed. This gauge is con-
trolled by the instrument cluster circuit board based
upon the cluster programming and electronic mes-
sages received by the cluster from the Powertrain
Control Module (PCM) over the Chrysler Collision
Detection (CCD) data bus. The speedometer is an air
core magnetic unit that receives battery current on
the instrument cluster electronic circuit board
through the fused ignition switch output (st-run) cir-
cuit whenever the ignition switch is in the On or
Start positions. The cluster is programmed to move
the gauge needle back to the low 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:
²Message Failure- If the cluster fails to receive
a speedometer message, it will hold the gauge needle
at the last indication for about four seconds, or until
the ignition switch is turned to the Off position,
whichever occurs first. If a new speedometer message
is not received after about four seconds, the gauge
needle will return to the far left (low) end of the
scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the gauge needle will be
swept to several calibration points on the gauge scale
in a prescribed sequence in order to confirm the func-
tionality of the gauge and the cluster control cir-
cuitry.
The PCM continually monitors the vehicle speed
sensor to determine the vehicle road speed, then
sends the proper vehicle speed messages to the
instrument cluster. For further diagnosis of the
speedometer or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). For proper diagnosis of the vehicle speed
sensor, the PCM, the CCD data bus, or the message
inputs to the instrument cluster that control the
speedometer, a DRBIIItscan tool is required. Refer
to the appropriate diagnostic information.
TACHOMETER
DESCRIPTION
A tachometer is standard equipment on all instru-
ment clusters. The tachometer is located just to the
left of the speedometer near the center of the instru-
ment cluster. The tachometer consists of a movable
gauge needle or pointer controlled by the instrument
cluster circuitry and a fixed 210 degree scale on the
gauge dial face that reads left-to-right either from 0
to 6 for gasoline engines, or from 0 to 4 for diesel
engines. The text ªRPM X 1000º imprinted on the
cluster overlay directly below the hub of the tachom-
eter needle identifies that each number on the
tachometer scale is to be multiplied times 1000 rpm.
The gauge scale of the gasoline engine tachometer is
red lined at 5000 rpm, while the diesel engine
tachometer is red lined at 3375 rpm. The diesel
engine tachometer also includes text that specifies
ªDIESEL FUEL ONLYº located just above the hub of
the tachometer needle. The tachometer graphics are
white and red against a black field, making them
clearly visible within the instrument cluster in day-
light. When illuminated from behind by the panel
lamps dimmer controlled cluster illumination lighting
with the exterior lamps turned On, the white graph-
ics appear blue-green, while the red graphics still
appear red. The orange gauge needle is internally
illuminated. Gauge illumination is provided by
replaceable incandescent bulb and bulb holder units
located on the instrument cluster electronic circuit
board. The tachometer is serviced as a unit with the
instrument cluster.
OPERATION
The tachometer gives an indication to the vehicle
operator of the engine speed. This gauge is controlled
by the instrument cluster circuit board based upon
the cluster programming and electronic messages
received by the cluster from the Powertrain Control
Module (PCM) over the Chrysler Collision Detection
(CCD) data bus. The tachometer is an air core mag-
netic unit that receives battery current on the instru-
ment cluster electronic circuit board through the
fused ignition switch output (st-run) circuit whenever
the ignition switch is in the On or Start positions.
The cluster is programmed to move the gauge needle
back to the low 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:
²Message Failure- If the cluster fails to receive
an engine speed message, it will hold the gauge nee-
dle at the last indication for about four seconds, or
until the ignition switch is turned to the Off position,
whichever occurs first. If a new engine speed mes-
8J - 30 INSTRUMENT CLUSTERBR/BE
SPEEDOMETER (Continued)

sage is not received after about four seconds, the
gauge needle will return to the far left (low) end of
the scale.
²Actuator Test- Each time the cluster is put
through the actuator test, the gauge needle will be
swept to several calibration points on the gauge scale
in a prescribed sequence in order to confirm the func-
tionality of the gauge and the cluster control cir-
cuitry.
The PCM continually monitors the crankshaft posi-
tion sensor to determine the engine speed, then
sends the proper engine speed messages to the
instrument cluster. For further diagnosis of the
tachometer or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). For proper diagnosis of the crankshaft position
sensor, the PCM, the CCD data bus, or the message
inputs to the instrument cluster that control the
tachometer, a DRBIIItscan tool is required. Refer to
the appropriate diagnostic information.
TRANS OVERTEMP
INDICATOR
DESCRIPTION
A transmission over-temperature indicator lamp is
standard equipment on all instrument clusters. How-
ever, on vehicles not equipped with the optional auto-
matic transmission, this indicator is electronically
disabled. The transmission over-temperature indica-
tor is located near the lower edge of the instrument
cluster overlay, to the left of center. The transmission
over-temperature indicator consists of a stencilled
cutout of the words ªTRANS TEMPº 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
lens behind the cutout in the opaque layer of the
overlay causes the ªTRANS TEMPº text to appear in
red through the translucent outer layer of the over-
lay when the indicator is illuminated from behind by
a Light Emitting Diode (LED) soldered onto the
instrument cluster electronic circuit board. The
transmission over-temperature indicator is serviced
as a unit with the instrument cluster.
OPERATION
The transmission over-temperature indicator gives
an indication to the vehicle operator when the trans-
mission fluid temperature is excessive, which may
lead to accelerated transmission component wear or
failure. This indicator is controlled by a transistor on
the instrument cluster circuit board based upon the
cluster programming and electronic messagesreceived by the cluster from the Powertrain Control
Module (PCM) over the Chrysler Collision Detection
(CCD) data bus. The transmission over-temperature
indicator Light Emitting Diode (LED) receives bat-
tery current on the instrument cluster electronic cir-
cuit board through the fused ignition switch output
(st-run) circuit whenever the ignition switch is in the
On or Start positions; 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 provided a path to ground by the instrument
cluster transistor. The instrument cluster will turn
on the transmission over-temperature indicator for
the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the transmission over-tem-
perature indicator is illuminated for about two sec-
onds as a bulb test.
²Trans Over-Temp Lamp-On Message- Each
time the cluster receives a trans over-temp lamp-on
message from the PCM indicating that the transmis-
sion fluid temperature is 135É C (275É F) or higher,
the indicator will be illuminated and a single chime
tone is sounded. The lamp remains illuminated until
the cluster receives a trans over-temp lamp-off mes-
sage from the PCM, 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 transmission over-tempera-
ture indicator is cycled off and then on again by the
appropriate trans over-temp messages from the PCM.
²Actuator Test- Each time the cluster is put
through the actuator test, the indicator will be
turned on during the bulb check portion of the test to
confirm the functionality of the LED and the cluster
control circuitry.
The PCM continually monitors the transmission
temperature sensor to determine the transmission
operating condition, then sends the proper messages
to the instrument cluster. If the instrument cluster
turns on the transmission over-temperature indicator
due to a high transmission oil temperature condition,
it may indicate that the transmission and/or the
transmission cooling system are being overloaded or
that they require service. For further diagnosis of the
transmission over-temperature indicator or the
instrument cluster circuitry that controls the LED,
(Refer to 8 - ELECTRICAL/INSTRUMENT CLUS-
TER - DIAGNOSIS AND TESTING). For proper
diagnosis of the transmission temperature sensor, the
PCM, the CCD data bus, or the message inputs to
the instrument cluster that control the transmission
over-temperature indicator, a DRBIIItscan tool is
required. Refer to the appropriate diagnostic infor-
mation.
BR/BEINSTRUMENT CLUSTER 8J - 31
TACHOMETER (Continued)

OPERATION
The upshift indicator gives an indication to the
vehicle operator when the transmission should be
shifted to the next highest gear in order to achieve
the best fuel economy. 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 Powertrain
Control Module (PCM) over the Chrysler Collision
Detection (CCD) data bus. The upshift indicator bulb
receives battery current on the instrument cluster
electronic circuit board through the fused ignition
switch output (st-run) circuit whenever the ignition
switch is in the On or Start positions; therefore, the
lamp will always be off when the ignition switch is in
any position except On or Start. The bulb only illu-
minates when it is provided a path to ground by the
instrument cluster transistor. On models not
equipped with a manual transmission, the incandes-
cent bulb and bulb holder unit are not installed at
the factory when the vehicle is built. The instrument
cluster will turn on the upshift indicator for the fol-
lowing reasons:
²Upshift Lamp-On Message- Each time the
cluster receives an upshift lamp-on message from the
PCM indicating the engine speed and load conditions
are right for a transmission upshift to occur, the
upshift indicator is illuminated. The indicator
remains illuminated until the cluster receives an
upshift lamp-off message from the PCM or until the
ignition switch is turned to the Off position, which-
ever occurs first. The PCM will normally send an
upshift lamp-off message three to five seconds after a
lamp-on message, if an upshift is not performed. The
indicator will then remain off until the vehicle stops
accelerating and is brought back into the range of
indicator operation, or until the transmission is
shifted into another gear.
²Actuator Test- Each time the cluster is put
through the actuator test, the indicator will be
turned on during the bulb check portion of the test to
confirm the functionality of the indicator and the
cluster control circuitry.
The PCM continually monitors the engine speed
and load conditions to determine the proper fuel and
ignition requirements. The PCM then sends the
proper messages to the instrument cluster. If the
upshift indicator fails to light during normal vehicle
operation, replace the bulb with a known good unit.
For further diagnosis of the upshift indicator or the
instrument cluster circuitry that controls the indica-
tor, (Refer to 8 - ELECTRICAL/INSTRUMENT
CLUSTER - DIAGNOSIS AND TESTING). For
proper diagnosis of the PCM, the CCD data bus, or
the message inputs to the instrument cluster that
control the upshift indicator, a DRBIIItscan tool isrequired. Refer to the appropriate diagnostic infor-
mation.
VOLTAGE GAUGE
DESCRIPTION
A voltage gauge is standard equipment on all
instrument clusters. The voltage gauge is located in
the upper left quadrant of the instrument cluster,
above the temperature gauge. The voltage gauge con-
sists of a movable gauge needle or pointer controlled
by the instrument cluster circuitry and a fixed 90
degree scale on the cluster overlay that reads left-to-
right from 8 volts to 18 volts. An International Con-
trol and Display Symbol icon for ªBattery Charging
Conditionº is located directly below the lowest grad-
uation of the gauge scale. The voltage gauge graphics
are white against a black field except for a single red
graduation at each end of the gauge scale, making
them clearly visible within the instrument cluster in
daylight. When illuminated from behind by the panel
lamps dimmer controlled cluster illumination lighting
with the exterior lamps turned On, the white graph-
ics appear blue-green and the red graphics appear
red. The orange gauge needle is internally illumi-
nated. Gauge illumination is provided by replaceable
incandescent bulb and bulb holder units located on
the instrument cluster electronic circuit board. The
voltage gauge is serviced as a unit with the instru-
ment cluster.
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 the cluster programming and elec-
tronic messages received by the cluster from the
Powertrain Control Module (PCM) over the Chrysler
Collision Detection (CCD) data bus. The voltage
gauge is an air core magnetic unit that receives bat-
tery current on the instrument cluster electronic cir-
cuit board through the fused ignition switch output
(st-run) circuit whenever the ignition switch is in the
On or Start positions. The cluster is programmed to
move the gauge needle back to the low 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:
²Charge Fail Message- Each time the cluster
receives a message from the PCM indicating a charge
fail condition (system voltage is 10.8 volts or lower),
the gauge needle is moved to the 8 volt graduation
on the gauge scale and the check gauges indicator is
illuminated. The gauge needle remains on the 8 volt
BR/BEINSTRUMENT CLUSTER 8J - 33
UPSHIFT INDICATOR (Continued)

graduation and the check gauges indicator remains
illuminated until the cluster receives a message from
the PCM indicating there is no charge fail condition
(system voltage is 10.9 volts or higher, but lower
than 16.7 volts), or until the ignition switch is turned
to the Off position, whichever occurs first. On models
equipped with the optional diesel engine, the instru-
ment cluster is programmed to support the voltmeter
gauge needle above the low end of normal graduation
and suppress the check gauges indicator operation
until ten seconds after the engine intake manifold air
heater has completed its cycle.
²Voltage High Message- Each time the cluster
receives a message from the PCM indicating a volt-
age high condition (system voltage is 16.7 volts or
higher), the gauge needle is moved to the 18 volt
graduation on the gauge scale and the check gauges
indicator is illuminated. The gauge needle remains
on the 18 volt graduation and the check gauges indi-
cator remains illuminated until the cluster receives a
message from the PCM indicating there is no voltage
high condition (system voltage is 16.6 volts or lower,
but higher than 10.9 volts), or until the ignition
switch is turned to the Off position, whichever occurs
first.
²Message Failure- If the cluster fails to receive
a system voltage message, it will hold the gauge nee-
dle at the last indication until a new message is
received, 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 gauge needle will be
swept to several calibration points on the gauge scale
in a prescribed sequence in order to confirm the func-
tionality of the gauge and the cluster control cir-
cuitry.
The PCM continually monitors the system voltage
to control the generator output. The PCM then sends
the proper system voltage messages to the instru-
ment cluster. For further diagnosis of the voltage
gauge or the instrument cluster circuitry that con-
trols the gauge, (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER - DIAGNOSIS AND TESTING). If
the instrument cluster turns on the check gauges
indicator due to a charge fail or voltage high condi-
tion, it may indicate that the charging system
requires service. For proper diagnosis of the charging
system, the CCD data bus, or the message inputs to
the instrument cluster that control the voltage
gauge, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.WAIT-TO-START INDICATOR
DESCRIPTION
A wait-to-start indicator is standard equipment on
all instrument clusters, but is only functional in vehi-
cles equipped with an optional diesel engine. The
wait-to-start indicator is located near the lower edge
of the instrument cluster overlay, to the right of cen-
ter. The wait-to-start indicator consists of a stenciled
cutout of the text ªWAIT TO STARTº in the opaque
layer of the cluster overlay. The dark outer layer of
the overlay prevents the indicator from being clearly
visible when it is not illuminated. A red lens located
behind the cutout causes the ªWAIT TO STARTº text
to appear in red through the translucent outer layer
of the overlay when the indicator is illuminated from
behind by a Light Emitting Diode (LED) that is sol-
dered 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 diesel engine intake
air heater is energized in its preheat operating mode.
This indicator is controlled by a hard wired input to
the instrument cluster from the Engine Control Mod-
ule (ECM). The wait-to-start indicator Light Emitting
Diode (LED) receives battery current on the instru-
ment cluster electronic circuit board through the
fused ignition switch output (st-run) circuit whenever
the ignition switch is in the On or Start positions;
therefore, the lamp will always be off when the igni-
tion switch is in any position except On or Start. The
indicator LED only illuminates when it is switched to
ground by the input from the ECM. The ECM will
turn on the wait-to-start indicator by pulling the
wait-to-start indicator driver circuit to ground each
time the ignition switch is turned to the On or Start
positions. The indicator then remains illuminated
until the ECM detects that the air within the intake
manifold is the proper temperature to ensure reliable
and efficient engine starting, until the ECM detects
that the engine is running, or until the ignition
switch is turned to the Off position, whichever occurs
first.
The ECM continually monitors the intake manifold
air temperature sensor, the Manifold Absolute Pres-
sure (MAP) sensor, and many other vehicle condi-
tions to determine when the wait-to-start indicator
should be illuminated. For proper diagnosis of the
wait-to-start indicator, the ECM, or the inputs the
ECM uses to control the wait-to-start indicator oper-
ation, a DRBIIItscan tool is required. Refer to the
appropriate diagnostic information.
8J - 34 INSTRUMENT CLUSTERBR/BE
VOLTAGE GAUGE (Continued)

(9) Disconnect the instrument panel wire harness
connector for the multi-function switch from the
switch connector receptacle. Check for continuity
between the hazard flasher signal circuit cavities in
the JB receptacle for the combination flasher and the
instrument panel wire harness connector for the
multi-function switch. There should be continuity. If
OK, go to Step 10. If not OK, repair the open hazard
flasher signal circuit between the JB and the multi-
function switch as required.
(10) Check for continuity between the flasher out-
put circuit cavities of the JB receptacle for the com-
bination flasher and in the instrument panel wire
harness connector for the multi-function switch.
There should be continuity. If OK, test the multi-
function switch. (Refer to 8 - ELECTRICAL/LAMPS/
LIGHTING - EXTERIOR/MULTI-FUNCTION
SWITCH - DIAGNOSIS AND TESTING). If not OK,
repair the open flasher output circuit between the JB
and the multi-function switch as required.
SPECIFICATIONS
EXTERIOR LAMPS
LAMP BULB
Back-up 3157
Cargo 921
Center High Mounted
Stop921
Clearance Roof Mounted 168
Fog Lamps 896
Headlamp - SLT 9004LL
Headlamp - Sport Low
Beam9007
Headlamp - Sport High
Beam9004LL
License Plate w/o
Bumper1155
License Plate -Step
Bumper168
Park/Turn Signal 3157NA
Snow Plow Control 161
Tail/Brake/Turn Signal 3157
Tail/Brake/Cab - Chassis 1157
Underhood 105
SPECIAL TOOLS
HEADLAMP ALIGNMENT
BRAKE LAMP SWITCH
DESCRIPTION
The plunger type brake lamp switch is mounted on
a bracket attached to the brake pedal support under
the instrument panel.
CAUTION: The switch can only be adjusted during
initial installation. If the switch is not adjusted prop-
erly a new switch must be installed.
OPERATION
The brake lamp switch is used for the brake lamp,
speed control brake sensor circuits and electronic
brake distribution (EBD). The brake lamp circuit is
open until the plunger is depressed. The speed con-
trol and brake sensor circuits are closed until the
plunger is depressed.
When the brake light switch is activated, the Pow-
ertrain Control Module (PCM) receives an input indi-
cating that the brakes are being applied. After
receiving this input, the PCM maintains idle speed to
a scheduled rpm through control of the Idle Air Con-
trol (IAC) motor. The brake switch input is also used
to disable vent and vacuum solenoid output signals
to the speed control servo.
Vehicles equipped with the speed control option use
a dual function brake lamp switch. The PCM moni-
tors the state of the dual function brake lamp switch.
Refer to the Brake section for more information on
brake lamp switch service and adjustment proce-
dures.
Headlamp Aiming Kit C-4466±A
8L - 4 LAMPS/LIGHTING - EXTERIORBR/BE
LAMPS/LIGHTING - EXTERIOR (Continued)

The brake switch is equipped with three sets of
contacts, one normally open and the other two nor-
mally closed (brakes disengaged). The PCM sends a
12 volt signal to one of the normally closed contacts
in the brake switch, which is returned to the PCM as
a brake switch state signal. With the contacts closed,
the 12 volt signal is pulled to ground causing the sig-
nal to go low. The low voltage signal, monitored by
the PCM, indicates that the brakes are not applied.
When the brakes are applied, the contacts open,
causing the PCM's output brake signal to go high,
disengaging the speed control, cutting off PCM power
to the speed control solenoids.
The second set of normally closed contacts supplies
12 volts from the PCM any time speed control is
turned on. Through the brake switch, current is
routed to the speed control servo solenoids. The
speed control solenoids (vacuum, vent and dump) are
provided this current any time the speed control is
ON and the brakes are disengaged.
When the driver applies the brakes, the contacts
open and current is interrupted to the solenoids. The
normally open contacts are fed battery voltage. When
the brakes are applied, battery voltage is supplied to
the brake lamps.
DIAGNOSIS AND TESTING - BRAKE LAMP
SWITCH
The brake lamp switch can be tested with an ohm-
meter. The ohmmeter is used to check continuity
between the pin terminals (Fig. 1).
SWITCH CIRCUIT IDENTIFICATION
²Terminals 1 and 2: brake lamp circuit
²Terminals 3 and 4: RWAL/ABS module and Pow-
ertrain Control Module (PCM) circuit
²Terminals 5 and 6: speed control circuit
SWITCH CONTINUITY TEST
NOTE: Disconnect switch harness before testing
switch continuity.
With switch plunger extended, attach test leads to
pins 1 and 2. Replace switch if meter indicates no
continuity.
With switch plunger retracted, attach test leads to
pins 3 and 4. Replace switch if meter indicates no
continuity.
With switch plunger retracted, attach test leads to
pins 5 and 6. Replace switch if meter indicates no
continuity.
REMOVAL
(1) Remove knee bolster for access to brake lamp
switch and pedal.
(2) Disconnect switch harness (Fig. 2) .
(3) Press and hold brake pedal in applied position.
(4) Rotate switch counterclockwise about 30É to
align switch lock tabs with notch in bracket.
(5) Pull switch rearward out of mounting bracket
and release brake pedal.
Fig. 1 Brake Lamp Switch Terminal Identification
1 - TERMINAL PINS
2 - PLUNGER TEST POSITIONS
Fig. 2 Brake Lamp Switch & Harness Connector
1 - BRAKE LIGHT SWITCH
2 - SWITCH BRACKET
3 - HARNESS CONNECTOR
4 - SWITCH LEVER
BR/BELAMPS/LIGHTING - EXTERIOR 8L - 5
BRAKE LAMP SWITCH (Continued)