1999 jaguar xk8 convertible. Fuel guage shows empty all the time. Is it the sending unit? Do you have to pull the gas tank to change it? How hard is that on these cars?

 

Because your fuel gauge is constantly reading empty, I would suspect a fuel level sensor which, as you describe, is the float or sending unit mounted in the front of the fuel tank. By all indications, the fuel tank must be removed for sensor replacement (possibly other forum members have an alternative). However, if you can get to the wiring of the sending unit it is basically a resistor measuring 900 ohms empty and 80 ohms full. There are a few areas in the forum that may be of assistance:
In the second Sticky of FAQ's, scroll down the alpabetical listing to Electrical - (subject) - Find your Electrical Diagrams and Information.
There you will find your vehicle's electical circuit diagrams.
Additionally, in the parts fiche section, there is a description of the sending unit.
And lastly, scroll down to Gus' section of fuel tank removal.

I think I would be tempted to take a rubber mallet and take a good "solid swing" around the sending unit on the fuel tank and hope the sending unit float was stuck. Probably not the proper procedure but sometimes it works?