Bad gas gauge?

Fill it up. pierce the casing on that blue wire ( shove shirt pin through it will work ) and check it with an ohm meter. You're looking for 10 ohms +/- .5. If you see 16 to 18 ohms the gauge is correct at 3/4 tank and the float on the sender has some fuel inside it.
Drive the gas out of it while waiting for a new sender to arrive.
If you do see 10 ohms the sender is correct and the gauge is likely the fault.
Pull the instrument panel and check the same blue wire for the same 10 ohms there. Correct 10 ohms there confirms the gauge is wrong.
If you dont get the same reading there you have a wire connection fault probably behind the left kick panel.