rodgerhartley wrote:
milescook, There are several possibilities. You mention applying power direct to the Starter/generator unit has variable results. I would suggest disconnecting the power lead at the starter. (Insolate it for safety), then apply power to that terminal and check for operation. Have a hand crank available and if NO function, reapply power to the unit terminal and give the crank a bit of a turn to see if it comes to life. There could be open segments on the armature. NOT GOOD. If no joy in this test likely will need to remove starter AND the switch for service. I wish you good luck. let us know what you find after this test.
Miles, Sorry to be late with this thought. In electricity a complete circuit is necessary. That means GROUND (irrespective to polarity) is as important as Power. Have you checked battery ground to frame (Transmission)? Try applying a ground cable to the right terminal on the starter/generator (close to engine) while applying Power to the outer terminal. Let us know the result.