Why wont my alternator charge

Yes they are different the 85 has the main large battery wire and 2 push on wires the 65 has 2 the large Battery wire and the other one is a flat spade coming from the regulator I also put the alternator from the 85 on the 65 of course i didn't hook up the 3rd terminal and it wasn't charging in the 65 but is charging like it should in the 85 the 85 alt should work in the 65 but the alternator from the 65 doesn't work in the 85 with out modification is that correct back to the cause of the 65 not charging at all is it most likely a bad ground or the voltage regulator could there be any other reason