Alternator or VR issue?

Well you tried, and you only, really, made one mistake

Instead of GROUNDING the alternator field terminal, you must jumper it to 12V. I would not use the alternator stud, because there can be an open in there that can lead you down "a path", ---the wrong one. "Rig" a wire direct either to battery pos. post or starter relay "big stud." If it charges, then it either has to be the VR, the green wire (which has happened!!) or the VR is not getting power under a load, meaning...........

CAVEAT........"Let's say" there is a poor connection where the blue IGN power wire is spliced. You might measure that with your meter DISconnected and it might show fine, but measuring it connected, the load from the field drawing current might "break" the bad connection.