1958 Ford 861 Tractor

make sure you are getting voltage to the coil. Also, make sure the wire going to the points (from the - side of the coil) is not grounding out anywhere (including inside the distributor if there is a little wire in there).

Also, you CAN convert to 12v. I did that on my 1950 DeSoto and it was fine for years...(until I sold it). many many people do it. Way cheaper on lights etc.... Starter will be fine.