- 1). Remove the starter or alternator from your vehicle. Follow the guidelines for your specific vehicle.
- 2). Place the starter or alternator on a flat work surface.
- 3). Set the multimeter to continuity mode. If your multimeter doesn't have a continuity mode set the ohms reader to the lowest level.
- 4). Check the commutator with a multimeter by placing the two probes on opposite ends of a single section of the armature. The meter should read a small level of resistance. If it reads infinite resistance the armature needs to be replaced. Repeat this for each section of the commutator.
- 5). Test the resistance from a single section of the commutator to the core by placing one probe on each. The resistance here should read infinite. If it doesn't then the armature needs to be replaced. Repeat this between every section of the commutator and the core.
- 6). Test the resistance from the commutator to the armature shaft. Place one multimeter probe on a section of the commutator and the other on the shaft. If there is infinite resistance then the armature is fine. If there is a small amount of resistance shown then the armature should be replaced. Repeat this for each section of the commutator.
- 7). Check the alternator slip rings. Place the multimeter probes on each of the slip rings. The meter should read between 2 and 4 ohms. If it doesn't then the alternator needs to be replaced.
- 8). Check the continuity from the battery to the alternator by placing one probe on the negative battery post (the black one) and one on one of the slip rings. The readout should be between 3 and 6 amps. A measure of zero indicates a bad alternator.
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