the stator frame (fig. 2-32) indicates the windings are
not grounded. It is not practical to test the stator for
shorts due to the very low resistance of the winding.
DIODE TESTING.With the stator windings
disconnected, each diode may be tested with an
ohmmeter or with a test light. To perform the test with
an ohmmeter, proceed as follows:
Connect one ohmmeter test lead to the diode lead
and the other to the diode case (fig. 2-33). Note
the reading. Then reverse the ohmmeters leads to
the diode and again note the reading. If both
readings are very low or very high, the diode is
defective. A good diode will give one low and
one high reading.
An alternate method of testing each diode is to use
a test lamp with a 12-volt battery. To perform a test
with a test lamp, proceed as follows:
Connect one of the test leads to the diode lead
and the other test lead as shown in figure 2-34.
Then reverse the lead connections. If the lamp
lights in both checks, the diode is defective. Or,
if the lamp fails to light in either direction, the
Figure 2-32.Testing a stator for grounds.
Figure 2-33.Testing diodes with an ohmmeter.
Figure 2-34.Testing diodes with a test lamp.
diode is defective. When a good diode is being
tested, the lamp will light in only one of the two
After completing the required test and making any
necessary repairs or replacement of parts, reassemble
the alternator and install it on the vehicle. After
installation, start the engine and check that the
charging system is functioning properly. NEVER
ATTEMPT TO POLARIZE AN ALTERNATOR.
Attempts to do so serves no purpose and may damage
the diodes, wiring, and other charging circuit
CHARGING SYSTEM TEST
Charging system tests should be performed when
problems point to low alternator voltage and current.
These tests will quickly determine the operating
condition of the charging system. Common charging
system tests are as follows:
Charging system output test-measures current
and voltage output of the charging system.
Regulator voltage testmeasures charging
system voltage under low output, low load
Regulator bypass testconnects full battery
voltage to the alternator field, leaving the
regulator out of the circuit.
Circuit resistance testsmeasures resistance in
insulted and grounded circuits of the charging
Charging system tests are performed in two
waysby using a load tester or by using a volt-ohm-
millimeter (VOM/multimeter). The load tester
provides the accurate method for testing a charging
system by measuring both system current and voltage.