Table 13-1. TROUBLESHOOTING
AMPS VOLTS DIAGNOSIS
HIGH LOW
Charging system is OK. Battery
is not yet fully charged. Wait for
charging system to bring to full
charge: AMPS should fall and
VOLTS should stabilize within
normal range.
HIGH NORMAL
Watch until AMPS fall, or VOLTS
exceed normal range. If AMPS
fall and VOLTS remain normal,
charging system is OK. If VOLTS
exceed normal, regulator and/or
field coil should be replaced
(Go to Static Tests).
HIGH HIGH
Stop test. Regulator and/or field
coil should be replaced.
(Go to Static Tests.)
LOW LOW
Make sure voltmeter leads are
attached at alternator. If
connections are OK, alternator
and/or regulator must be repaired
or replaced. Bypass regulator
(See Figure 13-3). If VOLTS
and/or AMPS rise, alternator is
OK and regulator should be
replaced. If no effect, repair
alternator.
(Go to Static Tests.)
LOW NORMAL Charging system is OK.
LOW HIGH
Stop test. If battery and voltmeter
check OK, regulator and/or field
coil must be replaced.
Table 13-2. VOLTAGE REGULATOR
SYSTEM
VOLTAGE
FACTORY
SETTING
NORMAL
RANGE
24
27.5 27.2 - 27.8
28.0 27.7 - 28.3
ON-VEHICLE TEST
Bypass Test:
Disconnect plug between alternator and regulator and
momentarily touch “F-“ terminal from alternator plug
to ground.
System voltage may rise above 32 volts on a 24
volt system, during regulator bypass test.
Possible damage to sensitive electronic compo-
nents could occur.
Refer to the "On Vehicle Troubleshooting Guide"
for an alternative to the bypass test.
FIGURE 13-2. VOLTAGE STEP ADJUST
1. Low 3. High
2. Medium
CAUTION!
USE HIGH SETTING ONLY FOR:
• EXTREME COLD
• INTERMITTENT SERVICE
• MAINTENANCE - FREE BATTERIES
CHECK BELT TENSION BEFORE ADJUSTING
VOLTAGE. TO ADJUST VOLTAGE, MOVE LINK TO
OTHER POST.
FIGURE 13-3.
1. F+ Stud (some units have F+ Stud & Phase taps)
M13003 04/01 Niehoff Alternator Overhaul Manual M13-7
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