Gas Gauge just Quit.......????

Common 12 volt test light might not show the approx' 5 volts that should be on the sender wire.
Yes there must be a chassis ground at the sender, whether factory jumper strap or otherwise. Maybe you tossed that ground strap, maybe you lost whatever was the ground path.
Maybe the fuel gauge is loose at its contact/mounting posts.
All good guesses. Let us know which was the best guess.