GMC 1976 ZEO 6083 Maintenance Manual page 400

6Y- 2 0 ENGINE ELECTRICAL
2. Battery using an excessive amount of water,
indicating an extremely high charging rate .
3. Excessive generator noise or vibration.
4. Failure of indicator lamp to illuminate when
ignition switch is turned on (engine not running) .
5 . Indicator lamp continues to glow with engine
running.
6. Indicator lamp fails to go out when ignition or
control switch is turned off.
The following is a list of the most common gener-
ator defects encountered :
1 . Open or shorted generator diodes .
2 . Open, shorted, or grounded stator winding.
3 . Open, shorted, or grounded field winding.
4. Worn generator brushes.
5. Excessive generator noise.
Generator diodes and stator windings should be
checked as explained under "Generator on Vehicle
Output Test" in Steb b, later in this section . If a
defect is indicated by this test, remove generator and
repair .
Excessive generator noise is usually the result of
one or more of the following:
1 . Brush "squeal" caused by a hard spot on one
of the brushes of rough or dirty slip rings. To check
for brush "squeal," remove generator drive belt and
spin generator drive pulley by hand . Lift brushes off
slip rings and spin drive pulley again . If noise disap-
pears, clean and inspect slip rings and replace
brushes if worn .
2. Dry or rough bearings in end frame.
CAUTION: Dry or rough bearings may be
the result of over-tightening generator drive
belt(s), loose generator mountings, oran un-
balanced generator fan or pulley.
3 . A defective diode or stator resulting in an elec-
trical unbalance.
STATIC CHECK
Before making any electrical checks, visually in-
spect all connections, including slip-on connectors,
to make sure they are clean and tight. Inspect all
wiring for cracked, frayed, or broken insulation . Be
sure generator mounting bolts are tight and unit is
properly grounded . Check for loose fan belt .
PRECAUTIONS
Observe the following precautions when per-
forming service operations on the alternating current
generating system . Failure to observe these precau
tions may result in serious damage to the charging
system .
NOTE:
A basic wiring diagram showing lead
connections is shown in Figure 24 .
1 . Electrical system is NEGATIVE GROUND .
Connecting the battery with positive terminal
grounded will result in severe damage to generator,
battery and battery cables .
2. DO NOT ground the field circuit at generator.
3 . Never operate generator with open circuit, that
is, with output wire disconnected from terminal and
with field circuit externally energized. Be absolutely
sure all connections in circuit are secure .
4. When using a booster battery, connect leads as
explained under "Jump Starting with Auxiliary
(Booster) Battery" in BATTERY (Sec . 6Y).
5 . Disconnect battery leads while charging bat-
teries . Do not use a fast charger as a booster for
starting the engine . When attaching battery charger
leads to battery, connect charger positive lead to
battery positive terminal and connect charger nega-
tive lead to battery negative terminal .
6. Do not short across or ground any of the termi-
nals in the charging circuit.
Figure 24-Typical Lead Connections