Field Coil Test

Check for continuity between the end of the field coil and yoke body. See Fig 1. Replace the field coil, if there is continuity.
Check continuity between the lead wire of terminal "C" and brush. See Fig 2. Replace yoke assembly if there is no continuity.

Fig 1: Checking Continuity Between Coil & Yoke
Courtesy of ISUZU MOTOR CO.

Fig 2: Checking Continuity Between Terminal "C" & Brush
Courtesy of ISUZU MOTOR CO.