On a difficult case like this one I'd use some jumpers directly: 8ga from alt to batt positive terminal (or starter relay), jumper from batt positive terminal to VE sense terminal. Jumper from batt to alt blue field wire male terminal. jumper from alt green field wire male terminal to VR side terminal. jumper from vr case to batt neg post and jumper from alt case to batt neg post. If it is now straight then remove 1 jumper at a time to pin down the offending circuit. If it's still acting up w all jumpers connected which is what I think it will be doing then that points to the alt. EDIT said VE but meant VR (voltage regulator)