(quoted from post at 10:56:59 05/05/15) Is it 6 volt or 12 volt? Generator or alternator?
Positive and negative ground is like right hand and left hand threads on a bolt. With bolts, the nut screws on in opposite directions, with positive and negative ground current flows through the system in opposite directions. With the bolt in many cases either direction will work, but there are cases where it must be one or the other.
A properly configured tractor electric system can be made to work either polarity. However, alternators, unless specially modified, must be negative ground. A generator regulator may be for positive ground only, negative ground only, or either ground configuration.
Proper connection of the battery, charging system, ignition coil, ammeter, and possibly fuel gauges are the only concern. Switches, points/condenser, starter, lights will work either polarity. (Later add ons such as radio or other attachments may specify a particular ground.)
“Would I hurt anything if I set it up with positive ground to see if it would work.” If you just reversed battery connections you would damage an alternator, or possibly the generator regulator
Your tractor has apparently been working and is still working OK. I say leave it alone, there is no problem with having it negative ground. In fact, negative ground has a big advantage in that it creates less confusion when jump starting with a modern 12 volt negative ground vehicle. If it fails to charge, ground polarity is not the problem.
