At the core of it is a mechanical latch mechanism. With it unlocked, do you feel resistance in the handle (as you squeeze it to open the tailgate), or does the handle feel like the door is locked all the time? No resistance says to me that something somewhere between the handle and the latching mechanism itself is broken, or that the latch never unlocks. Infinite resistance (that is, you can't squeeze the handle all the way) says to me that something is jammed.