Everyone needs to verify that the vehicle (tractor/whatever) is in fact negative ground. Many of the older IHC equipment were positive ground. But, that itself needs to be confirmed because many restorations included updating from 6V positive ground to 12V negative ground. Though, they could be kept as 12V positive ground. Just note which battery terminal leads to chassis ground initially. If it is positive, then one could put the switch on the positive side.