Jon, it's been quite a while since I've been into the circuitry on a balancing-coil gauge, bit if the dash unit goes to "full" when the tank sensor wire is grounded, it's likely that it's seeing zero resistance or close to it. Real hands-on experience trumps what seems to be logical every time, though!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!