Once in a while over the years, something like this would occur with one of my old Chev V8 starting systems and, if I KNEW that the battery was good and had power elsewhere (lights/radio/horn that did not dim or go off when cranking) I would figure it to not be a battery ground issue, so would bypass the IGN switch (only had one autotrans with NSS) and if that did not enable it to spin or even click, I would assume the problem to be the solenoid. That particular solenoid has a plunger/disc setup that can burn/melt/get dirty - or a lead in there might melt or break loose - or otherwise fail to plunge and work. If rebuilding the solenoid parts or installing a new one did not make it spin, I would ask a bunch of experts for help.
