1996 mustang tempeture gage wont work?
Pull the wire off of the sensor and ground it. The gauge should peg at full scale. If if does not, either the gauge is faulty or the wiring between the sensor and the gauge is faulty. Isolate that by checking the sensor wire with an ohm meter. It should read 0 ohms end-to-end. If it does not, clean the connections or replace it as needed. If it does read 0 ohms, the gauge is faulty.
The fact that the gauge goes to center scale when you turn on the engine does not necessarily mean that the gauge is working properly. It's a center-weighted gauge that has 2 internal windings. If one of them is open it will either go to center scale and never move again, or will not move at all from the power-off position.
If the gauge DOES deflect when you ground the sensor wire, the sensor is either bad or was improperly installed. If you used ordinary gasket sealer on it it may be insulated from ground and the gauge will not work. You can get special electrically conductive sealant to install screw-in temp sensors or you could remove it and clean off as much of the sealer as possible and install it with a VERY light amount of sealer. Check for continuity between the body of the sensor and any clean ground point. It should show 0 ohms.
There's also a chance that the instrument panel voltage regulator is bad, but if that fails, both the fuel gauge and the temp gauge will fail. If the fuel gauge is working properly, that's not likely the problem.
Ignore the fist response. It's absurd.