If the tractor has been converted to 12V with an alternator, it has to be negative ground. If it's still 6V with a generator it won't make a lot of difference. As long as the tractor starts and runs ok, it really doesen't care which way the battery is installed. The biggest problem is coil polarity. The ignition coil will work best if the correct polarity is observed. If the tractor has a mag, this is out of the picture, as the mag does not require power from the battery. I suggest you connect the battery Positive ground if it's still 6V or if it's 12V with a generator. If it's 12V with an alternator, leave it negative ground. If it has a battery ignition and you change the ground to positive, be sure to connect the coil with the proper polarity. Is that about as clear as mud? Feel free to email me if you need more info.