Mike - Try testing the generator using the procedure in the article, Testing a Dynamo/Generator in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ If the generator will not put out 20 volts using this procedure, then the generator is bad. Take it to a good auto electric shop for repair.
Cheers,
Dave
http://homepages.donobi.net/sufuelpumps/