GMC 4000 Series Service Manual page 424

Figure 3 — Two-Unit Type Regulator with Cover Removed
pipe plug in cover and rotating the adjusting screw
within regulator as explained later in this section.
PRECAUTIONS
Observe the following precautions when per­
forming service operations on the alternating cur­
rent generating system . Failure to observe these
precautions may result in serious damage to the
charging system .
1. THE ELECTRICAL SYSTEM IS NEGATIVE
GROUND. Connecting the battery or a battery charg­
er with the positive terminal grounded will en­
danger generator diodes and vehicle wiring by high
current flow. Burned wiring harnesses and burned
"Open" diodes will result.
2. Never operate the generator on an open
circuit (field terminal connected and output term ­
inal disconnected). With no battery or electrical
load in the circuit (open circuit) the generator can
build-up excessively high voltage. Be sure all con­
nections in the charging circuit are secure.
3. When working near the generator or regu­
lator and before replacing electrical system com­
ponents, disconnect negative lead from battery to
prevent accidental shorting at generator and regu­
lator terminals where battery voltage is available.
NOTE: Replace voltage regulator with same
type and model.
4. The generator cannot be polarized. Any at­
tempt to polarize the generator may result in se r ­
ious damage to charging system components.
5. Do not short across or ground terminals
on generator or regulator.
G M C S E R V I C E M A N U A L
connect negative battery terminals together and
positive terminals together.
batteries. Do not use a fast charger as a booster
for starting the engine. When attaching battery
charger leads to the battery, connect charger posi­
tive lead to battery positive terminal and connect
charger negative lead to battery negative terminal.
fore welding on vehicle since a reverse current
flow from the welder may damage generator diodes
as well as other electrical components.
special resistance wire in harness connected to
ignition control switch unless it is of the same
material and of same length (approx. 60 inches
long). Generating system will not function without
this wire. Wire is identified on wiring diagrams
in applicable "Wiring Diagrams" booklet as 24-
BN.-WS. Resistance value of wire is approximately
10 - 1.0 ohms, 6.25 watts.
Analysis Chart" later in this section to aid in lo­
cating source of charging system malfunctions
before replacing components.
cause of a malfunction to prevent reoccurrence.
A/C GENERATING SYSTEM
A C C ESS PLUG TO
VOLTAGE ADJUSTMENT
Figure 4 — Full Transistor Type Regulator (Typical)
6. When using a booster battery, be sure to
7. Disconnect battery leads while charging
8. Disconnect battery negative terminal be­
9. Never replace the brown and white stripe
NOTE: Refer to "Charging System Trouble
IMPORTANT: Always locate and correct the
Sec. 6Y
Page 413