Chapter A: General Diagnosis
32
Field Current Draw Test
The field current draw test is performed with the engine
off. For some vehicles, the regulator or warning lamp cir-
cuit, or both, may need to be bypassed while testing.
Check the Service Manual for specific instructions. To
test current draw, connect an ammeter either between
the positive battery terminal and the generator field or
between the field and ground. Then switch the ignition
on without starting the engine, or bypass the ignition
switch and warning lamp with a jumper wire as direct-
ed, and read field current draw on the ammeter. If out of
specifications, remove the generator for further testing.
If the ammeter reading fluctuates, service the brushes
and windings.
This test is performed only on charging systems that
have an external voltage regulator. Do not attempt this
test on the internal regulator.
Voltage Regulator Test
Check the regulated voltage with a voltmeter connect-
ed between the generator output terminal and ground,
or between the positive battery terminal and ground.
Start and run the engine at a fast idle for several minutes
to stabilize the charging system. The amperage charge
rate into the battery should be low. If voltage readings
are too low, confirm the amperage output at the gener-
ator before condemning the voltage regulator. High gen-
erator amperage output can cause a low voltage read-
ing. If the readings are too high, replace the voltage
regulator.
If any of the above tests indicate an generator problem,
the generator must be removed from the vehicle for ser-
vicing. For additional information on bench testing and
repairing generators, refer to Book A6, "Electrical and
Electronic Systems" of this series.
System Inspection
Charging system complaints often result from simple
and easily corrected problems that become obvious
during a quick visual inspection of the system compo-
nents.
To begin:
1. Check the battery electrolyte level, state-of charge,
and capacity. If the battery is worn out or defective,
the charging system may not be at fault.
2. Inspect the generator drive belt. Loose belts are a
major cause of poor charging system performance.
If the belt is loose or damaged remove it for further
inspection. Loosen the tension on the belt before
attempting to remove it from the engine. Never
force or pry a belt a belt over pulley flanges. While
the belt is removed, examine the pulleys for dam-
age or misalignment. Replace pulleys and install
the new belt. Belts must be properly tensioned. A
loose belt will slip and a tight belt can damage
bearings. Adjust tension to specifications. After in-
stalling a new drive belt, allow the engine to run for
at least 10 to 15 minutes. Switch the engine off,
then recheck and adjust belt tension using "used"
belt specifications.
3. Check all system wiring and connections. Be sure
to inspect fusible links, and make sure multiple
connectors are latched properly. Even when the
fusible link looks good it may be damaged inter-
nally. If in doubt pull on one end of the fusible link.
If the insulation stretches replace the link. Discon-
nect each connector in the circuit and conduct a vi-
sual inspection. Look closely for damaged, corrod-
ed or pushed out pins. Use a new terminal pin to
check for a snug fit into the plug. If the socket in
the plug is loose replace with a new part. Recon-
nect and ensure the connector is latched properly.
If the circuit is physically sound continue with a
voltage drop test.
4. Inspect the generator and regulator mountings for
loose or missing bolts. Replace or tighten as need-
ed.
Correct any problems discovered during the inspection.
If system performance remains below specifications,
isolate the cause by performing system tests.
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