1984 ltd fuel gauge always at half full?

I would assume that if there was a short in the sending unit circuit, your gauge would indicate either full or empty. Therefore, I am leaning towards your sending unit being stuck at 1/2.

One test you could perform would be to disconnect the connector to the sending unit and jump the signal wire to ground and see if you get full scale deflection on your gas gauge. If you get full scale deflection, then you can assume that your circuit is ok and that the sending unit must be at fault.

Here is Señor Car guy doing some basic sending unit diagnostics:

[video]http://www.youtube.com/watch?v=bBjkw8yl1vQ[/video]

You might try unplugging the connector in the trunk, turn on the key, and observe the gauge. If you get a different reading then it’s likely the problem is in the sending unit in the tank.