Dodge RAM TRUCK 1500 1995 Service Manual page 414

8E - 4 INSTRUMENT PANEL AND GAUGES
running, the tachometer receives an engine speed
pulse signal from the Powertrain Control Module
(PCM). An electronic integrated circuit contained
within the tachometer reads and analyzes the pulse
signal. It then adjusts the ground path resistance of
one electromagnet in the gauge to control needle
movement. Frequency values for the pulse signal are
shown in a chart in Specifications.
TRIP ODOMETER
The trip odometer is driven by the same electronic
integrated circuit as the speedometer/odometer. How­
ever, by depressing the trip odometer reset knob on
the face of the speedometer, the trip odometer can be
reset to zero. The trip odometer is serviced only as a
part of the speedometer/odometer gauge assembly.
VOLTMETER
The voltmeter is connected in parallel with the bat­
tery. With the ignition switch ON, the voltmeter in­
dicates battery or generator output voltage,
whichever is greater.
INDICATOR LAMPS
Indicator lamps are located in several areas of the
cluster and instrument panel, depending upon equip­
ment. Those lamps within the cluster area are served
by the cluster printed circuit and cluster connectors.
AIRBAG INDICATOR LAMP
The airbag indicator lamp is switched to ground by
the Airbag Control Module (ACM). The lamp lights
for 6 to 8 seconds each time the ignition switch is
turned to the ON position as a bulb test and to indi­
cate a system self-test is in process. If the lamp re­
mains on after the self-test or comes on while
driving, it may indicate that the ACM has detected a
system malfunction or that the system has become
inoperative. Refer to Group 8M - Restraint Systems
for more information.
ANTI-LOCK BRAKE SYSTEM LAMP
The Anti-Lock Brake System (ABS) or Rear Wheel
Anti-Lock (RWAL) lamp is switched to ground by the
ABS or RWAL module. The module lights the lamp
when the ignition switch is turned to the START po­
sition as a bulb test. The lamp will stay on for up to
30 seconds after vehicle start-up to indicate a system
self-test is in process. If the lamp remains on after
start-up, or comes on and stays on while driving, it
may indicate that the ABS or RWAL module has de­
tected a system malfunction or that the system has
become inoperative. Refer to Group 5 - Brakes for
more information.
BRAKE WARNING LM$P
The brake warning lamp warns the driver that the
parking brake is applied or that the pressures in the
two halves of the split brake hydraulic system are
unequal. With the ignition switch turned ON, battery
voltage is supplied to one side of the indicator bulb. A
ground path for the bulb is provided by up to 5
switches. The bulb will light when:
• the brake warning switch is closed (indicating un­
equal brake system hydraulic pressures possibly due
to brake fluid leakage)
• the ignition switch is in the START position (bulb
test)
• the vacuum sensor (diesel engine) senses low sys­
tem vacuum
o certain ABS or RWAL system faults are detected
o the parking brake switch is closed (parking brake
is applied).
Refer to Group 5 - Brakes for more information.
FOUR-WHEEL
DRIVE INDICATOR
LAMP
On vehicles with four-wheel drive, the indicator
lamp lights when the front axle disconnect is con­
nected in a 4WD operating mode. Voltage is supplied
to one side of the indicator bulb. A switch in the front
axle disconnect housing is connected to the other side
of the indicator bulb. When the switch is closed, a
path to ground is provided and the indicator bulb
lights.
HAZARD WARNING INDICATOR LAMP
This lamp is used only on certain export models.
The lamp in the message center is turned on by a
signal from the hazard warning (multi-function)
switch to indicate that the hazard warning lamp sys­
tem is activated.
HEADLAMP HIGH BEAM INDICATOR LAMP
The high beam indicator lamp is controlled by the
headlamp dimmer (multi-function) switch. One side
of the indicator bulb is grounded at all times. The
other side of the bulb receives battery feed through
the contacts of the dimmer switch when the multi­
function switch stalk is actuated to turn the head­
lamp high beams on. Refer to Group 8L - Lamps for
more information.
LOW FUEL WARNING LAMP
The low fuel warning lamp will light when the fuel
level falls below approximately 4 gallons. One side of
the low fuel warning bulb is grounded at all times. A
low fuel warning circuit attached to the rear of the
gauge cluster provides battery voltage to the lamp
when the fuel level is low. The low fuel warning mod­
ule monitors the signal from the fuel level sending
unit. When the circuit senses approximately 65 ohms
or more from the fuel level sender for 10 to 20 con­
tinuous seconds, the indicator will light. The indica­
tor will remain on until the circuit senses