I was kinda wondering that myself! I do know that my 48 Ford 8N is Positive ground and my 46 Chevy is negative. The Ford tractor runs better Positive ground (yes, I "polarized" the VR). I also have a 1967 BSA motorcycle that was positve ground. It ran better when I switched it to Negative ground.

http://scroungeman.blogspot.com/
1947 3/4 ton Pickup