I have a Ford 900 series (not sure of the exact model). It is currently not running but I would like to get it that way. There is not a battery in the tractor at the moment. Did the 900 series come standard with a 6 volt or a 12 volt system? Were they positively or negatively grounded? and how do I tell if someone has already upgraded to a 12 volt system if that was not original? thanks for any help you can give me.