HEAVY DUTY ALTERNATORS
If the alternator is found to be OK or if an
"overcharging" condition exists, then the regulator
must be adjusted. See VOLTAGE REGULATOR
NOTE - If the alternator Is equipped with a "fixed
adjustments cannot be made. If the alternator is
found to be OK, the "fixed voltage" regulator must
If adjustment has no effect on the output voltage, the
regulator must be replaced.
To establish which component is causing the
alternator to malfunction, perform an AC voltage test.
The batteries must be fully charged and a 12-volt test
lamp is needed to perform this test. The test lamp
can be made of a two filament headlight unit, with
both filaments wired in parallel. The lamp acts as an
indicator as well as a load. With all electrical
accessories off, run the engine at about 1000 RPM
and connect the test lamp across the three AC
terminals as shown in Figure 4.
If the test lamp does not light, or if it lights with equal
intensity on each phase, then the rotor is probably
faulty. If one or two test points result in a dimmer
light, then either the stator or a power diode is
Figure 4 - AC Voltage Test.
The voltage regulator used in these alternators is a solid state
device and for this reason will normally have an extremely long
life. It can, however, be damaged by mechanical or electrical
If the system polarity is inadvertently reversed by installing a
battery backwards, boosting or jump starting with the jumper
connected backwards, or reversing the positive and negative
alternator output leads when changing an alternator, the
voltage regulator will be damaged. Although the polarity
reversal may only be momentary and may not damage the
alternator diodes, the regulator will still be damaged.
VOLTAGE REGULATOR ADJUSTMENT
NOTE - This procedure applies to alternators with
adjustable regulator. If the alternator Is equipped with a
"fixed voltage" regulator, adjustment cannot be made.
Check the drive belts, wiring, and mounting hardware,
and make sure that they are in proper working order.
Check the batteries according to manufacturers
specifications to insure that they are in good
condition. The batteries must be fully charged. If
necessary, charge or replace batteries.
To adjust the regulator, shut off all electrical
accessories and run the engine at about 1000 RPM.
Check the voltage across the alternator output
terminals. Remove the plastic screw from the
regulator and engage a small screwdriver with the
adjustment screw inside the access hole (Figure 5).
CAUTION - TO AVOID DAMAGING REGULATOR,
DO NOT EXERT EXCESS PRESSURE ON THE
Figure 5 - Adjusting Voltage Regulator.
Turn the adjustment screw CLOCKWISE TO RAISE voltage or
COUNTERCLOCKWISE TO LOWER the voltage.
CAUTION - TO AVOID DAMAGING REGULATOR, DO NOT
FORCE THE ADJUSTMENT SCREW PAST THE STOPS AT
EITHER END OF THE ADJUSTMENT RANGE.
Voltage should be set between 13.8-14.2 volts (or 14.0 volts
nominal setting ± 0.2 volts). Reinstall the plastic
CTS-4043A - Chapter II - Page 4