PS -- does your truck have a MagicAire type heater or the old Ford type? In either case, I fear the fan may run backwards if you go neg. ground. Wipers, too.

 

Before I fried the regulator, the heater and wipers worked correctly with negative ground. The ammeter is backwards, but I can't figure out how to switch it. It's the old style with the wire passed through an induction loop, not a hot and ground wire.

 

Ammeter is easy - disconnect the wire, pull it out of the loop on the ammeter, push it thru the loop the opposite direction and reconnect it.