Because this is a safety related issue, in that it can potentially be a fire hazzard if not correctly repaired, I would recommend having this diagnosed by a professional near you. I WOULD NOT recommend that you diagnose this and/or attempt to repair it yourself. To answer the question, though, typically when a voltage regulator fails, it does not charge at all. You could have faulty diodes inside the generator causing the boil over. Have it checked by a professional.