Hi,
The voltage regulators on the 6 volt systems have 2 sets of points in them, I think the 12 volt voltage regulator has 2 sets of points also. I don't have a 12 volt one to look at.
The points in the 6 volt ones get burned, or corroded, then the generator won't charge.
You could look at the points in yours, file them if they look burned or corroded.
Wipe off all filings with a clean rag. Sometimes they work, and sometimes they still don't work.
Disconnect the battery ground cable before working on the voltage regulator.
There is a Flow Chart that we use on here, to diagnose problems with the charging system. It is for 6 volt Cubs. I don't know if it is the same as a 12 volt system would use.