Changed the battery and now the fuel guage does not work

It sounds like you do not have a good ground connection between the fuel pump (possibly mounted inside the fuel tank) and the chassis/neg side of the battery. This is sometimes caused by rust on mounts etc. I would try test connecting a wire from the negative/chassis side of the battery directly to the fuel pump chassis/mount. Good luck!

I'm assuming this has dual tanks, do you know if it is not working on both tanks ?
Most people would check the circuit for the gauge at the tank. The sending unit grounds the gauge on the dash.

To confirm if the fault is with the Rheostat float within the fuel tank or the fuel guage in the dashbboard, you can remove the wiring to the fuel tank float. If the guage reading changes- to full- then the guage is good and the fault can be a jammed rheostat which can be removed from the tank and replaced after draining the tank. The guage can be tested on the outside with a ground wiring to the plate of the fittings and as the float is moved the guage must show a change in reading. if not the voltage must be measured to confirm the working of the guage.

the guage can be fixed by changing the fuel pump. actually if the pump is installed incorrectly then the guage will eventually go out. just had the same issue and i changed my pump and it worked.

sounds like a bad earth some were have a look at battery terminals both ends even the one on the body work if thats ok look at engine earths as well, if all this fails have your battery tested it could have a dud sell in it or even the carging system could be playing up, then again it could just be a bad conection were it clips into the steedo head,,, any bad wiring could cause this

clog in your fuel line or you need to change your fuel filter.

todays fuel pumps have the signal gauge togethoir the only way is to change the fuel pump

If sender is new in the fuel tank, you have a wire problem between conection of fuel sender and dashboard gauge most likely place at dasbboard gauge.

This is not a calibration issue, the sender in the fuel tank is the problem, this is a common symtom for senders when they fail

check the cluster fuse inside the car its abbreviated most likely as like clstr or clsr if you just unplug the battery it will reset the computer..