GMC 1976 ZEO 6083 Maintenance Manual page 399

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 normal-
ly, proceed to "Undercharged Bat-
tery" or "Overcharged Battery" sec-
tion . Otherwise, proceed to either
one of the following three abnormal
conditions :
Switch On, Lamp Off, Engine Stopped
- This condition can be caused by the
defects listed in "Switch Off, Lamp
On" under "GENERATOR TROUBLE-
SHOOTING," or by an open in the
circuit .
To determine where an open exists,
check for a blown fuse, a burned out
bulb, defective bulb, or an open in
No. 1 lead circuit between generator
and ignition switch.
OVERCHARGED BATTERY
1 . To determine battery condition, see "Battery Service
And Diagnosis" earlier in this section .
2 . Connect a voltmeter from generator No. 2 terminal
to ground . If reading is zero, No. 2 lead circuit is
open .
3 . If battery and No . 2 lead circuit check good, but an
obvious overcharge condition exists as evidenced
by excessive battery water usage, proceed as follows :
a .Separate end frames as covered in "Disassembly"
under heading of "GENERATOR REPAIR ." Check
field windingfor grounds and shorts . If defective,
replace rotor and test regulator with an approved
regulator tester .
b . Connect ohmmeter using lowest range scale from
brush lead clip to end frame; then reverse lead
connections .
c .If both readings are zero, either the brush lead
clip is grounded or regulator may be defective .
d . A grounded brush lead clip can result from omis-
sion of insulating washer, omission of insulating
sleeve over screw, or damaged insulating sleeve .
Remove screw to inspect sleeve . If satisfactory,
test regulator with an approved regulator tester.
GENERATING SYSTEM DIAGNOSIS
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 "UNDER-
CHARGED BATTERY" on this page .
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
between these two leads . If the lamp
goes out, replace the rectifier bridge
as covered in the "GENERATOR RE-
PAIR ." This condition will cause an
undercharged battery .
If no defects are found, proceed to
"UNDERCHARGED BATTERY" above .
If ampere output is within 10 amps of
rated output as stamped on generator
frame, generator is not defective ;
recheck Steps 1 through 5 .
If test hole is accessible, ground the
field winding by inserting a screw-
driver into the test hole .
CAUTION : Tab is within 3/4-inch of
casting surface . Do not force screw-
driver deeper than 1-inch into end
frame .
Operate engine at moderate speed as
required, and adjust carbon pile as
required to obtain maximum current
output.
If output is not within 10 amps of rated
output, check the field winding, diode
trio, rectifier bridge, and stator as
covered in "GENERATOR REPAIR ."
UNDERCHARGED BATTERY
This condition, as evidenced by slow cranking andlow
specific gravity readings, can be caused by one or
more of the following conditions even though the in-
dicator lamp may be operating normally . The follow-
ing procedure also applies to circuits with an am-
meter .
1 . Insure that the undercharged condition has not been
caused by accessories having been left on for ex-
tended periods .
2 . Check the drive belt for proper tension .
3 . If a battery defect is suspected, see "Battery Service
And Diagnosis" earlier in this section.
4 .Inspect the wiring for defects . Check all connec-
tions 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, 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 voltmeter
connection and battery .
6 . If previous Steps 1 through 5 check satisfactorily,
check Delcotron Generator as follows :
a . Disconnect battery ground cable .
b . Connect an ammeter in the circuit at the "BAT"
terminal of the generator .
c . Reconnect battery ground cable .
d .Turn on radio, windshield wipers, lights high
beam and blower motor high speed . Connect a
carbon pile across the battery .
e . Operate engine at moderate speed as required,
and adjust carbon pile as required, to obtain
maximum current output .
If amperes output is not within 10 amps
of rated output, determine if test hole
is accessible .
If test hole is not accessible, disas-
semble generator and make tests
listed in "GENERATOR REPAIR ."
If output is within 10 amps of rated
output, test regulator with an approv-
ed regulator tester, and check field
winding as covered in "GENERATOR
REPAIR ."
Generating System Diagnosis
ENGINE ELECTRICAL
6Y- 1 9