Bench Testing

Rotor

1. Set ohmmeter on x1000 scale and check rotor windings for grounds. See Fig 1. Connect one ohmmeter lead to rotor shaft and second lead to each slip ring. Resistance should be infinite. If not, replace rotor.
   Fig 1: Testing Rotor on Bench for Grounds & Opens

   Courtesy of GENERAL MOTORS CORP.
2. Set ohmmeter on x1 scale and test rotor for opens. Connect an ohmmeter lead to each slip ring. See Fig 1. Resistance should be 1.7-2.3 ohms. If not, replace rotor assembly.

Stator

1. Unsolder stator leads at 3 terminals on rectifier bridge. Remove stator. Set ohmmeter to x1000 scale. Check for grounds. Connect one ohmmeter lead to stator frame and other lead to each stator lead. Resistance should be infinity. If reading is not infinity, stator is grounded and must be replaced.
2. To check for open conditions, set ohmmeter on x1000 scale. Attach ohmmeter leads to any 2 stator leads. Check each combination of stator leads in succession. If any ohmmeter reading is infinity, a winding is open and stator assembly must be replaced.

Rectifier Bridge

1. With alternator disassembled, connect one ohmmeter lead to grounded heat sink (closest to outside of alternator housing). Connect second ohmmeter lead firmly against flat metal portion of terminal connector (not threaded stud). See Fig 2. Reverse leads to same heat sink and terminal. If readings are identical, replace rectifier bridge.
   Fig 2: Testing Rectifier Bridge

   Courtesy of GENERAL MOTORS CORP.
2. If one high and one low reading is obtained, rectifier bridge is okay. Repeat test between grounded heat sink and 2 flat metal connectors. Test between insulated heat sink (closest to inside of alternator) and each of the 3 flat metal connectors.
3. Check remaining bridge rectifiers in same manner. DO NOT  replace rectifier bridge unless one pair of readings are the same.