Alternator: Testing and Inspection

Fig. 1 Testing rotor coil resistance:

Alternator must be removed from vehicle for testing.

1. Connect an ohmmeter between ``E'' and ``F'' terminals, Fig. 1.
2. If resistance is higher than 5 ohms, poor continuity exists between brushes and commutator.
3. If no continuity exists between ``E'' and ``F'' terminals, check for open in rotor coil circuit, sticking brush or broken lead wire.
4. If resistance is lower than 5 ohms, this may be an indication of rotor coil layer short of circuit being grounded.

Fig. 2 Positive diode test connections:

5. Connect positive lead of ohmmeter to ``N'' terminal and negative lead to ``A'' terminal, Fig. 2. If continuity exists between terminals, one or more of the three positive diodes are shorted.

Fig. 3 Negative diode test connections:

6. Connect positive lead of ohmmeter to ``E'' terminal and negative lead to ``N'' terminal, Fig. 3. If continuity exists between terminals, then one or more of the three negative diodes are shorted.