Are your battery cables hot? Sounds like a ground to me as well. If you have the common grounding strap for 6 volt, you might disconnect it from where it is grounded to the frame and wire brush it to make sure you are getting a good ground. Mine did that before and the cables got hot as well. Once it was cleaned off, it was fine. I'd check both terminals for corrosion while you're at it. Don't know much about generators as mine has an alternator, but could it be worn brushes? Probably not, but just a thought. Somneone else will know better than me on that.
