Gas gauge not working

Could be a lot of things. First thing, as mentioned above, ground the sending unit wire to the frame, is the gauge goes up then the gauge is fine. If it doesn't it's probably your gauge. If it does go up then it's in your sending unit. Most common problem is the float doesn't float anymore, so pull the sending unit and see if it has fuel in it. Floats are cheap (I sell them for $12 free shipping) while the entire unit is expensive ($50-100 depending on vendor, Van's Auto is cheapest). If the float is fine then you need to test the sending unit. Put a Ohm meter on the pin (you also have to ground it) and see what the gauge does as it runs through it's swing, you should see a nice swing of Ohms from low to high and back as you swing it. If you have good Ohm readings then the sending unit is fine. Sometimes you will get some gaps in the readings and that means the coil wire inside the unit it worn. Sometimes you can clean them, sometimes you will need to replace it. Also as mentioned above the sending unit needs to be grounded, should be a wire clamp thing that goes from the sending unit to the fuel line. The rubber line isolates it so you need this ground. Hope that helps!