2005 mountaineer fuel gauge
 

I don't think you can access it without dropping the fuel tank, but before you count everything as bad, check the wires going to and from the gas tank. make sure the harness is securely snapped together. check for any local ground wires and make sure they are securely attached. sometimes this happens because something is loose and reconnecting it will fix it. It also happens to be due to running over something and that something cutting a wire.

also, check your fuses. sometimes the fuel gauge is fused with other items (like on my mgm, it's on the same circuit as the cornering lights that my car is not equipped with but still wired for and my e-brake crushed one harness and shorted it out due to the tape holing the mass of wires together getting old and coming loose. I doubt that's anywhere near what happened to yours, but check the fuses anyhow to make sure).