GMC 1976 ZEO 6083 Maintenance Manual page 620

CHASSIS ELECTRICAL 12- 1 5
Disconnect wire from sender unit and attach AC-GG3 tester between this wire
and chassis ground .
Position ignition switch to "ON."
1 . With tester knob set at "Continuity," lamp should glow .
2 . With tester knob set at "0," dash unit should indicate "0" psi .
3 . With tester knob set at "90," dash unit should indicate "full scale" pressure .
4 . If 1, 2, and 3 above are OK, clean
sender terminal to
insure good
electrical contact
with wire and
make sure sender unit is ground-
ing to engine .
5. If pressure gauge system is still
not functioning properly after com-
pleting Step 4, replace sender unit .
DO NOT START ENGINE .
AC-GG3 TESTER
6 . If any one of 1, 2, and 3 are not OK,
check wiring and all connections
(including grounds) .
7 . If any one of 1, 2, and 3 are still
not OK after completing Step 6,
replace dash unit .
A-1791
Figure 20-Engine Oil Pressure Gauge Diagnosis (Method Using AC-663 Tester)