The alternator black wire must go to earth at or near the regulator so if you can determine the black wire with the ring termination goes to the alternator (physical check....) thats fine. Mind you do you know if the alternator works (or the regulator too)??
That sounds reassuring, looking on the wiring diagram I wondered if there was supposed to be a third terminal on the regulator. I've followed that wire to the alternator so hopefully all is ok with that one. When the engine was running when I looked at the car before purchase the ignition light worked as expected, when I get it running again I'll be able to check the alternator properly.