Field Coil Open Test
WARNING: This page is about a different car, the 1996 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
Remove armature from frame and field assembly. Using self-powered test light, place one lead on field lead connection and other lead on one insulated brush. See Fig 1. Test light should illuminate. If test light does not illuminate, field coil is open. Repair or replace field and frame assembly. Repeat test for each insulated brush.