GMC 4000 Series Service Manual page 430

positive terminal and regulator No. 3 terminal,
and jumper lead is connected between regulator
No. 2 and No. 3 terminals.
b. Connect a voltmeter between battery ground
terminal and ground on regulator base as shown
in View B, Part 2, figure 14, and record the volt­
age drop.
c. Add voltage in Step a. to voltage in Step b.
above. If total voltage (a. + b.) is above 0.25 volt,
check system wiring for high resistance and check
regulator for proper ground.
d. If total voltage in Step c. is below0.25 volt,
connect a voltmeter between regulator No. 3 term ­
inal and ground on regulator base as shown in
View C, figure 14; then with switch on, operate
engine at 1,275 rpm for 15 minutes. Leave cover
on regulator. Place a thermometer %-inch from
regulator cover and compare voltage with "Speci­
fications" given in "Temperature Chart" at end of
this section.
4. If voltage is not within specified range, re­
move access plug from regulator cover and note
position of plastic screw slot beneath the plug. The
slot will be aligned with one of the divisions or
lines cast on the regulator cover.
If actual regulating voltage, as checked, is not
within the voltage range specified for the measured
ambient temperature, repair or replace the regu­
lator.
5. If voltage is within specified range for the
measured ambient temperature, the charging sy s­
tem operation is satisfactory. However, the regu­
lator setting may need to be changed to meet bat­
tery charging requirement for a particular type of
operation. Remove plug from regulator cover, then
use a thin, flat-bladed instrument to turn the slot­
ted adjuster inside the regulator (fig. 15).
6. To raise the voltage setting, turn slotted
adjusting plug one notch (clockwise), then check
for an improved battery condition.
NOTE: After two notches in each direction
there is a positive stop.
7. To lower the voltage setting, turn slotted
adjusting plug one notch (counterclockwise), then
check for an improved battery condition after a
service period of reasonable length.
8. If regulator cannot be adjusted to a value
within the specified range, repair or replace the
regulator.
NOTE: If repeated regulator failures are ex­
perienced on the vehicle, but no defects are found,
a shorted, grounded, or open generator field wind­
ing, or grounded leads of an intermittent nature
should be suspected.
TAILORING THE VOLTAGE SETTING
The proper setting is obtained when the battery
remains fully charged with a minimum use of water.
G M C S E R V I C E M A N U A L
remains undercharged, raise the setting by 0.3
volts, then check the battery over a period of time
to see if improvements were achieved; reset reg­
ulator if necessary. If the system is overcharging,
lower the setting by 0.3 volts, then check battery
over a period of time.
vehicles using A.C. generators, the replacement
A/C GENERATING SYSTEM
If any circuit defects are found, yet the battery
GENERATOR REPLACEMENT
Due to variations in design and equipment on
Figure 14— Connections for Testing 1116374 or
1116378 Regulator Voltage Setting (Typical)
Sec. 6Y
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