Rotor Field Winding Test

To check for grounds, attach ohmmeter leads to shaft and slip ring (each ring in turn). If reading is not infinity, replace rotor.
To test for open field, attach ohmmeter leads to each slip ring. Resistance should measure about 2.4-3.5 ohms. If not, replace rotor.

Fig 1: Rotor Bench Test For Open or Short Circuit

NOTE: Delco 15 SI and 27 SI alternators have delta stator windings and cannot be checked for open circuit.