Fuel Gauge Doesn't Work
 

I have an 88 RX-7 and the fuel gauge isn't reading anything.. The gas light comes on when it gets low so I'm wondering if it's the fuel gauge itself or something to do with the sending unit in the tank? The screws to get into the tank are completely stripped it's going to be a pain to get in there so I wanna know what other possibilities could be causing this. If anyone has any ideas that'd be great because it's kind of annoying lol.. Thanks!