I'm assuming you've tested for continuity across the fuel gauge posts? That could save you prying the case open.
Ok, maybe I missed it, but if you're running 12v and you don't have a resistor on the (+) side of the fuel gauge, it's toast. The monofilament coil that moves the needle will vaporize. I had dropped mine, broke the coil at the post, and reattached it with a fine-tipped soldering iron and a pair of flatjaw heatsinks. If it's melted, you may not have enough wire left to work with. Good luck.
If you have a multimeter, it can tell you how all the individual bits are working. You don't need anything fancy, mine cost about $2. If all else fails, head over to the Swap Meet.
