So why the service techs needed a 3 position tester... The sender wire direct to ground zero ohms test doesn't always prove good gauge. I've seen some that were soooo toasted inside that zero ohms could cause movement while within normal range ohms could not. Looking at those, the needle doesn't go all the way home at off. It'll stop very near the hash mark scale.
This 4th/off/home needle position isn't on the tester.
