1986 Chevy G30 Trans Van

My fuel gauge is pegged past full when the car is off or on. I've found the ground from the top of the tank to the body and drilled a new hole, cleaned all the metal, attached a new eyelet connector to the wire, and reattached and still nothing changed. I understand I may need to drop the tank to reach the sending unit and most of the wires on top. My question is, if the battery is disconnected, should the gauge still be reading full? If there is no power moving through the sending unit, and therefore no electrical resistance to be read despite the float being up, wouldn't there be nothing to read at the gauge? Could this indicate the gauge is the issue? I'll be honest, I'm doing what I can to avoid having to drop the tank haha. Any help would be greatly appreciated.

 

It been my own experience that the sender is the issue in 90 percent of these kinds of repairs. not the dash gauge. Yeah, dropping a fuel tank is never fun, but if you can get the gasoline out it's much easier, of course. That said it might be the gauge. There is always the 10 percent.fact.