GMC 1976 ZEO 6083 Maintenance Manual page 401

7. Do not attempt to polarize the generator.
8. When working near generator or regulator,
disconnect battery cable to prevent accidental
grounding at generator terminals.
9. Always disconnect battery negative cables
when replacing electrical system components . This
eliminates accidental shorting at generator terminals
where battery voltage is available.
10. Disconnect battery negative cables before
welding on vehicle, since a reverse current from the
welder may damage generator diodes as well as other
electrical components .
11 . Never replace the special resistance wire in
harness connected to the ignition switch unless it is
of same material and of same length (approx. 60
inches long). Generating system will not function
without this wire . Wire is identified in Engine and
Chassis Wiring Diagram (Back of Manual).
NOT Close adherence to the Troubleshooting Proce-
dures in order presented will lead to location and
correction of charging system malfunctions in the
shortest time possible . Only a portion of the proce-
dures need to be performed in order to locate the
trouble.
ON VEHICLE TESTS
FAULTY INDICATOR LAMP OPERATION
Check the indicator lamp for normal operation as
shown below.
Switch
Lamp
Engine
OFF OFF STOPPED
ON ON STOPPED
ON OFF RUNNING
If the indicator lamp operates normally, proceed
to "Undercharged Battery" or "Overcharged Bat-
tery" section. Otherwise, proceed to either one of the
following three abnormal conditions .
1. Switch
Off, Lamp
On-In this case, disconnect
the two leads from the generator No. 1 and No. 2
terminals. If the lamp stays on, there is a short be
tween these two leads. If the lamp goes out, replace
the rectifier bridge as covered in the "GENERA-
TOR REPAIR" section. This condition will cause
an undercharged battery.
2. Switch On,
Lamp Off,
Engine Stopped-This condi-
tion can be caused by the defects listed in Part 1
above, or by an open in the circuit. To determine
where an open exists, proceed as follows :
ENGINE ELECTRICAL
6Y- 2 1
a. Check for a blown fuse, a burned out bulb,
defective bulb socket, or an open in No. 1 lead circuit
between generator and ignition switch .
b. If no defects have been found, proceed to
"Undercharged Battery" section.
3. Switch On,
Lamp
On, Engine Running-Check for a
blown fuse (where used) between indicator lamp and
switch . The other possible causes of this condition
are covered in the "UNDERCHARGED BAT-
TERY" section .
If a defect has been found and corrected at this
point, no further checks need be made.
UNDERCHARGED BATTERY
This condition, as evidenced by slow cranking
and low specific gravity readings, can be caused by
one or more of the following conditions even though
the indicator lamp may be operating normally .
1 . Insure that the undercharged condition has
not been caused by accessories having been left on for
extended periods.
2. Check the drive belt for proper tension.
3. If a battery defect is suspected, check per appli-
cable battery service and diagnosis given earlier in
this section .
4. Inspect the wiring for defects. Check all con-
nections for tightness and cleanliness, including the
slip connectors at the generator and firewall, and the
cable clamps and battery posts.
5. With ignition switch on and all wiring harness
leads connected, connect a voltmeter from :
a. generator "BAT" terminal to ground
b. generator No. 1 terminal to ground
c. generator No. 2 terminal to ground
A zero reading indicates an open between voltm-
eter connection and battery . NOTE : An open No. 2
lead circuit on early production generators caused
uncontrolled voltage, battery overcharge and possi-
ble damage to battery and accessories . Generators
supplied for later applications have a built-in feature
which avoids overcharge and accessory damage by
preventing the generator from turning on if there is
an open in the wiring harness connected to the No.
2 generator terminal . Opens in the wiring harness
connected between the No. 2 generator terminal and