Why wont my alternator charge
^^READ CAREFULLY^^ What Bobzilla posted
Up through 69, alternators should have ONLY ONE field terminal, the other brush is factory grounded with no accessible terminal
HOWEVER it is popular nowadays for rebuilders/ sellers to sell you 70 and later alternators which are properly called "isolated field" (not "dual field") and which have TWO insulated brush/ field terminals.
As above, if you have the original type 69/ earlier regulator, you must ground one of the two field terminals. Connect your green field wire as normal