IH farm and heavy equipment used to use a positive ground....why? I don't know.
British built. Back in the '60's, we had a B-414, my uncle had its smaller brother, a B-275, both were 12 volt POSITIVE ground, compliments of Lucas electrical systems. Made jump starting a real pain!
Years later, IH changed all their machines over to Delco-Remy, even the imports.
All our other IH equipment, from a 1947 Farmall H to our 3388, were all negative ground, though the H was 6 volt, all the rest were 12 volt.