I am going to call the fluctuating ammeter needle resolved. I believe the problem was the fine wire flexible conductor to one of the brushes was barely touching the gen case....close enough that engine vibration was enough to intermittently cause the wire to just touch the case (to ground) and thus cause the gen to tend go to full output towards the + side of the ammeter. Which it always did. After pushing the wire well clear of the case, the ammeter is now completely calm with a charging voltage at 13.8.
Thanks all for your thoughts
