To answer your initial question. If the push button switch has one terminal, it is using the chassis as a ground return. Like Jerry's suggestion.
If it has two terminals, it is breaking hot.(your tractor type)

I have used the Ford relay on many Chevys. I think it's what Wrenchbender posted.


Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn