[AT] Tractor batteries

[Greg Hass]

Was looking at some old tractor stuff online and was reminded of 
something I  have know for years but have never, at least in my failing 
memory, seen a plausible explanation as to why most 6 volt tractors have 
positive grounds whereas 12 volt tractors have negative ground.  At 
first I thought it could be because 6 volts had generators, however, our 
first 12 volt tractors had generators and later models had alternators 
so that doesn't seem to be the reason. Any and all answers would be great.
      Greg Hass