Alternator: Testing and Inspection

Fig. 4 Checking contact between brushes and commutator:

1. Measure resistance across terminals ``F'' and ``E,'' Fig. 4. Resistance should be 5 ohms.
2. If resistance is greater than 5 ohms, there is poor contact between brushes and commutator.
3. If there is no continuity, rotor coil circuit is open, one of the brushes is sticking or the lead wire is broken.
4. A resistance of less than 5 ohms indicates a short in the rotor coil layer or a short in the circuit being grounded.

Fig. 5 Testing positive diodes:

5. Connect tester positive lead to ``N'' terminal and negative lead to ``A'' terminal, Fig. 5. If there is no continuity, one or more of the diodes on the positive side are shorted.

Fig. 6 Testing negative diodes:

6. Connect tester positive lead to ``E'' terminal and negative lead to ``N'' terminal, Fig. 6. If there is no continuity, one or more of the diodes on the negative side is shorted.