GMC 4000 Series Service Manual page 426

W IR IN G H A R N E S S
C O N N E C T O R
Figure 5 — Jum per Lead Connections for Testing
Indicator Lamp Circuit (TypicalI
GENERATOR CHARGE INDICATOR
LAMP CIRCUIT TEST
NOTE: Refer to procedure outlined in "Charg­
ing System Trouble Analysis Chart" later in this
section to determine whether something other than
a generator or regulator defect is indicated before
proceeding with this test which applies to vehicles
equipped with a charge indicator lamp.
1. Check the indicator lamp bulb which may be
burned out. Make sure socket is fully engaged.
2. Check wiring connections at junction.
3. Lift the regulator terminal latch slightly,
then pull connector from regulator terminals.
CAUTION: DO NOT allow any leads
to contact a ground or "live" wire or term­
inal except as directed. A heavy cloth,
taped In position below regulator term­
inals, will assist in preventing contact.
4. Referring to figure 5, insert jumper lead
(J-9782-1) into #4 terminal socket in harness con­
nector and ground the other end to regulator base
as illustrated. Momentarily (not more than 10 se c ­
onds) turn on ignition or control switch. Indicator
lamp should light. If not, check for open circuit in
wiring between the jumper lead and switch, switch
and horn relay, and to the battery.
5. If indicator lamp com es on when #4 socket
in wiring harness connector is grounded (fig. 5),
connect jumper lead between wiring harness con­
nector term inals "F" and #4 as shown in figure 6.
Turn ignition or control switch on momentarily.
a. If light comes on, an open circuit exists
within the regulator. Refer to regulator tests later.
b. If light does not come on, an open circuit
exists between the connector and generator or in
the field circuit within generator.
G M C S E R V I C E M A N U A L
-9 7 3 3
tpm
A /C GENERATING SYSTEM
W I R I N G H A R N E S S
C O N N E C T O R
Figure 6 — Checking Indicator Lamp W iring
c. Use a long jumper lead between the #4
socket in harness connector and the "F" (field)
terminal at generator. If light then comes on, the
generator field circuit is good and an open circuit
exists in wiring between "F" terminal on regulator
and "F" terminal on generator. If light does not
come on, an open circuit exists in the generator
field circuit.
6. If, with all wiring connected normally, and
the indicator lamp comes on when ignition or con­
trol switch is off, a defective diode is indicated.
GENERATOR OUTPUT TEST
ON VEHICLE
Refer to procedures outlined in "Charging
System Trouble Analysis Chart" later in this se c ­
tion to determine whether something other than a
generator defect is indicated before proceeding
with this test.
QUICK TEST FOR OUTPUT
1. Connect voltmeter "POS" lead to generator
Figure 7 — Connections for Testing Generator Output
Sec. 6Y
Page 415
Jumper
Lead
T P M -9 7 3 4