My gas gauge is always on full.It never moves any more. Is there some way I can check the sending unit without droping the tank?

 

The wire(s) that come from the sending unit to the gauge are probably broaken. Happened to me once, the wire was under the car near the gas tank. Dont know if thats the place you will find yours, previous owner did a lot of custom (stoopd) work on the car.
Hope this helps.

 

the sending unit may have gone bad as well. I cant remember the way it is on our cars, it will either read full or empty when the two wires are touching for the gauge. It will do the oposite if they are open but Im thinking yours has an open somewhere in the wiring or it may be a bad sending unit.

 

You can measure the resistance in the sender and the wire going forward, by disconnecting the wires at the connector which is near the tank. It is the one you have to undo to get the tank out. You can see is there is a short going forward to the gauge, or open circuit or short circuit at the sender end.

You put the ohm meter contacts into the wires after you disconnect them. The wires supplying the power to the fuel pump are grouped with the sensor one.