Using an ohmmeter, measure resistance, between each diode lead and upper rectifier body. Perform STEP 1. See Fig 1. Check resistance in both directions by reversing ohmmeter leads. Resistance should be more than 5 ohms in one direction and less than 5 ohms in the other direction. If resistance is not as specified, replace rectifier.
Using an ohmmeter, measure resistance, between each diode lead and lower rectifier body. Perform STEP 2. See Fig 1. Check resistance in both directions by reversing ohmmeter leads. Resistance should be more than 5 ohms in one direction and less than 5 ohms in the other direction. If resistance is not as specified, replace rectifier.
Using an ohmmeter, measure resistance between diode trio leads. Perform STEP 3. See Fig 1. Check resistance in both directions by reversing ohmmeter leads. Resistance should be more than 5 ohms in one direction and less than 5 ohms in the other direction. Replace rectifier if resistance is not as specified.

Fig 1: Testing Generator Rectifier

Courtesy of GENERAL MOTORS CORP.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Rectifier Test