I checked with the guy in the area who does nothing but gauges and instrument clusters. He walked me through a self-test utility where you hold down the button thingy while turning the key to "on", then push the button again for a gague sweep. ALL gagues swept. He told me the gauge is fine. The shop that installed the lift pump also rebuilt the engine. The tech made sure the sending unit was plugged in, plugged in their diagnostic tablet and it showed 99% full tank. So we're getting signal from the sending unit and the gauge is working. I called FASS and he told me there's really no way to wire it wrong. I'm at a loss and I really need this gauge to work. If anyone reading this has any idea of what to check next, please advise. Thank you.