1983 full size chevy truck Gas guage always reads full How do you fix?

Answer 1

Unbolt bed, raise it by putting a bucket between bed and the frame giving yourself access to the top of the fuel tank.  Remove the the multiple bolts on the plate where the electrical wires go in.  This will be your float device in your fuel tank.  Most likely it needs replaced.  You can look around those wires to insure they are not gashed and grounded it somewhere.