Si Series: Rotor

Set ohmmeter on x1000 scale. Check rotor windings for grounds. See Figure. Connect one ohmmeter lead to rotor shaft and second lead to each slip ring. Resistance should be very high (infinity). If resistance is not as specified, replace rotor assembly.

Fig 1: Bench Testing Rotor for Grounds and Opens
Courtesy of GENERAL MOTORS CORP.
Set ohmmeter on x1 scale and test rotor for opens. Connect an ohmmeter lead to each slip ring. See Fig 1. Resistance reading should be 2.4-3.5 ohms. If resistance is not as specified, replace rotor assembly.