Well coach like they say "spit happens"! You can look up the resistance of the sending unit and compare it to what you have now... But in similiar situations I have always simply installed a new sender and it has always been the culpret. So Id advise purchasing a new one and installing it to see if the gauge goes back to work for you.
There is a central ground for all the gauges so usually if one does not work ALL fail.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist