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9-54
1977 PONTIAC SERVICE MANUAL
Fig. 9-66 Digital Clock
TRIP ODOMETER (FIG. 9-67)
The trip odometer used on A, G and X Series is reset
by pulling the knob out and turning until all zeroes appear.
A
new style trip odometer is available on the B Series.
It can be reset by twice fully depressing the pushbutton
located on the right side of the speedometer cluster. The first
depression shows all zeroes, and the second locks them in
position. Both depressions must be done to avoid possible half
cycling of the trip odometer. A slow, steady push should be
used to avoid damage to the internal mechanism.
On both styles, do not reset the odometer with the
vehicle in motion. Damage to the odometer may occur.
Fig. 9-67 Trip Odometer
DIAGNOSIS
NOTE: Always check the fuse first before proceding
with diagnosis.
TACHOMETER
1 . Insure that the in line fuse is not blown.
2. With ignition off, on H and HM Series, remove the
tachometer from the cluster to gain access to the connecters.
On G, A, F and
X,
disconnect the connecter from the back
of the instrument panel. Turn ignition on and check for 12
volts at the ignition input connecter (pink) and no voltage at
ground (black). Connect a test light to the brown wire which
connects to the "TACH" terminal of the distributor. With
the engine idling, a test light should light with approximately
the same intensity as a 12 volt signal. As the engine speed
increases, the test light intensity should decrease.
3. If proper signals are present at the connecter, replace
the gage. If not, the problem is in the wiring to the gage.
OIL PRESSURE GAGE
1. Disconnect the wire at the sending unit on the engine.
With igntion on, gage should register past 80 psi.
2. With ignition on, use a jumper wire to short the
connecter to ground. Gage should now read below 0.
3. If gage reads properly in steps 1 and 2, replace the
sending unit. If it does not, the trouble is either in the gage
or the wiring to the gage.
4. Noticeably improves FM reception. should be ground,
ignition voltage, and signal. The signal input should be
checked with an ohmmeter, and should indicate continuity
(0 ohms) with the connecter at the sender shorted to ground,
and no continuity (infinite resistance) with the connecter at
the sender disconnected. If these checks are ok, replace the
gage. If not, repair the problem in the wiring.
5. The gage may also be checked by substituting a
resistence source for the sender. The gage should read
approximately 0 psi at 1 ohm and 80 psi at 88 ohms.
VOLTMETER
1 . Remove the gage as shown in On-Car Service.
2. With ignition on, terminal connecters to the gage
should indicate electrical system voltage and ground. If they
do, replace the gage. If they do not, repair the problem in the
wiring.
WATER TEMPERATURE GAGE
1 . Disconnect the wire at the temperature sender on the
block. With ignition on, gage should read below 100°F.
2. Use a jumper wire to short the wire to ground. With
ignition on, gage should deflect full scale, well past 260°F.
3. If the gage reads properly in steps 1 and 2, replace the
sender. If it does not, the problem is either in the gage or the
wiring.
4. Remove the gage as shown in On-Car Service. With
ignition on, the terminal connecters should read ground,
electrical system voltage and signal. Check for continuity as
shown for oil pressure gage. If these check ok, replace the
gage. If not, repair the wiring problem.
5. The gage may also be checked by substituting a
resistence source for the sender. The gage should read 100°F.
at 350 ohms, 220°F. at 68 ohms, and 260°F. at 46 ohms.
CLOCK
1 . Remove the clock as shown in On-Car Service, or
disconnect wiring to it.
2. With igntion o f f , clock should receive battery voltage
at one terminal and ground at the other. If it does not, replace
the clock.
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