usually meters read 0 when they're not hooked to anything - if it's an original gauge the sender should be 0-30 ohms, so the meter needs to be on a low range .... not really clear what you're measuring, how are you "grounding the gauge"?
with ignition off you should be putting one of the meter leads to ground, then the other lead to the brown wire [sender], that should read the sender resistance - if there's no reading check at the tank, if you can't weasel the meter probe in to the sender terminal, use a safety pin to poke into the wire near the tank and put the meter probe on that, if you get a reading there the wire is bad, sender to gauge .... if you can't prove the sender works and check what the resistance range is, you won't have any idea what gauge to buy
Bill
