It has been in the upper 90º here in Minnesota, to hot to work in the garage last week. jJust got back to the problem this weekend.
The last test I did was to disconnect the cable from the starter and hook the positive (+) jumper to the starter and battery, and connect the negative (-) cable to the engine block. I connected the other end of the jumper to a battery and the starter attempted to turn until the engine came up to compression then it would not turn thru compression and crank the engine. I am looking for a four brush starter.