On Wednesday, December 23, 2015 at 10:16:00 AM UTC-6, Uncle Monster wrote:

I was thinking that the tractor may have its own earth ground, like an implement dug into the soil and there is some weird ground loop or some strange potential from the electrical power system getting through the positive connection of the charger.

....ease-up on the meds! —–|—”—¡—‰|——