The fuel gauge on my 1985 FLTC reads a 1/2 tank when the tank is full...what could be causing this?

 

The sending unit in the tank could be corroded. They are simple variable resistors. Take it out of the tank, clean the contact surfaces, make sure there is good contact. Put a multimeter on it and move the float up and down and see if you're getting good resistance. I'm assuming you have the same thing as in my '88, which I think you do.

 

Thanks, I'll check it out.

 

Yeah, most likely the sender. Be sure to check that the float isn't full of gas too.

 

Check the float for fuel inside it .
Clean the resistor with carb. cleaner and make sure the wiper contact is pressing on the variable resistor , they get weak and sometimes need a bit of a bend to ensure good contact when it travels back and forth across the resistor. Use a multi meter to check this.