UncleBrad, I was an auto mechanic during the late 70's. From that experience, I seem to remember that some engine starters only have one positive terminal. The negative terminal is the starter case.
If this is true for your starter, then there is only one large (>300 amp, >3/8") terminal that is connected to the positive brushes. The negative brushes are connected to the series field. The series field is then connected to the starter case internally.
If this is the case, then you should be able to make the following ohmic readings:
- lift all brushes: positive terminal, armature, and case are all isolated from each other.
- install positive brushes only: positive terminal is common to armature, case is isolated from armature and positive terminal.
- install negative brushes only: positive terminal is isolated from armature and case, armature and case are common.
If these tests confirm that you have a series connected, single terminal, starter motor, then you can run it by doing the following.
Connect the power supply between the positive terminal and the starter case. When you do this, the starter should run and there should be no spark between the case and ground (assuming the power supply ground equals the real ground.)
However, as MikeHalloran suggested, do not do this for long since the speed without load for a series motor is high enough to destroy the motor. Also, fasten the motor to something solid since the acceleration torgue of the starter will make it jump and roll when it is engaged.
Of course, my auto mechanic experience was a long time ago. At the time, I knew nothing about motors and very little about electricity. So, I hope this helps but, please forgive me if I am wrong.