My 89 yo neighbor told me that his 39 9n would not start his weekend so his nephew jumped it with a 12 volt battery.  Now it does not appear to be charging.  I am a little mystified with the 6V positive ground system.  Should the terminal on the generator test positive for continuity to ground or should it be isolated from ground.  When I first started the tractor the ammeter was showing discharge and so was my meter connected to the terminal on the generator.  What did these guys do??