Starter/Gen Problems

[adiexp]

Hi
Not sure if anyone can help just changed my old 88 Flathead motor for a new honda gx engine. I descided to use my starter/generator for ease (cost). All seemed OK then I noticed my battery was boiling over, checked the voltage at the battery and it was over 20volts done some checking then found that when I reved up the engine the voltage on the white wire from the starter/generator was 20volts or more. then I checked on the yellow wire and there was nothing on the wire. I assume there should be a voltage on this wire as I assume this feeds into the voltage regulator to control the voltage. Does anybody know what sort of voltage there should be on the wire or any ideas what else to check.

Thanks Adie