The gauges do not go bad very often. As you found out, it is usually a bad cable. Try to pull the cable out of the housing, it might just slide right out if there is no clip on the other end. If it comes out put some grease on it and put it back in. Slide it in till it stops and then try to turn it,if it starts to turn gently push in while slowly turning and it will slip in the square drive at the transmission end. You are done.
Put the gauge back on. This is the best way to prevent the cable from breaking. It may not slide out from the gauge end, in that case I would not worry about it unless you have the transmission cover off and you can get to the other end.