Its the micro switch in the tail gate handle. part number :cenad160 3.55$ in canada,dont know in the states.
You need to take off the back door trim,just by pulling it off, theres about 10 body clips holding it,then you take the off two bolts(10mm) retaining the handle,and you have 2 torx screw(size is 27) on the side of the door to remove, to get the handle out.
You disconnect the wire,take a small flat head screwdriver and slide off the retainning clip and the little micro-switch from the handle.
When you get the new one,fill up the handle insert with dielectric grease,slide in the new micro-switch wich comes with the wiring,and reinstall everything back together.
You are done my friend!
That should be the problem,the switch isnt insulated,and humidity gets into the switch insert in the handle,wich makes corosion and breaks the switch,this is why i put some dielectric grease in it just to get it waterproof,i did mine just yesterday,wasnt working anymore since last december,and now,well,everything is working like new,easy reliable fix 
