Those were the options to replace my nonfunctioning regulator. My brother went to Autozone and was told you can tell because they have 6 wires coming out but both models do and there are no markings on mine. Is there a way to tell from the generator? The book shows the wire terminal orientation as being identical for 40 and 55. I'm curious how they work if anyone knows. THere seems to be some resistence wire that I'm guessing would vary with difference in current. Rosco