Charging system question. What is the correct Excitation Voltage to rotor?

My 1984 moto guzzi v65 has not been charging. I found that the excitation voltage is less than one volt. I believe the alternator may be good and the voltage regulator is actually the problem. Replacement regulators are only $17 so I ordered a that first.I applied an external 12v directly to the brushes and the alternator created voltage with the bike running, so it appears the excitation voltage should be 12v?This has been a fun engineering problem to have, as it applies to larger power plants. via /r/CafeRacers https://www.reddit.com/r/CafeRacers/comments/bdjw1f/charging_system_question_what_is_the_correct/?utm_source=ifttt