rear defroster

I want to hook a rear defroster, but the wiring is not there. There is a dummy button in the place of the defroster button. I don't know what I need. I have a rear defroster back glass.

Sounds like the hatch was replaced at one time.

Look at the wiring diagram for the car. It will show what color wires are used for the defroster. The wiring may be there, just not hooked up. If you trace the circuit for the defroster, it will show what relays are required and how they should be connected.