pull a batt cable off (always a good habit to get into when using the ohm function on the meter). Pull the L connector off of the sending unit threaded nub at the tank & from that wire to a KNOWN good ground you should show either no continuity (infinity) if it is correct & we know it ain't but not zero/several tenths which is a dead short which means that blue wire is improperly grounded somewhere forward from where you are at up to the downstream side of the gauge. EDIT If you show a dead short then unplug the connector behind the dr kick panel which will open that circuit & repeat the test back at the sender. if still grounded then the ground is rearward from the kick panel connector. If not then it's grounded somewhere from the kick panel connector upstream to the round plug in/flat printed circuit board/gas gauge case