From the thread I linked:
Ok! Wife and kid left and I cracked a cold one and went for it.
I verified on my build sheet that I had : "Tailgate Ajar Warning Lamp"
I did NOT have it on my window sticker.
Confirmed it to be CBC Config IO F pin 26 Connector F Pin 26: Trunk/Liftgate Ajar Signal Input Present: No
Changing to YES has me working!
Overhead bed lights now coming on when I open the gate as well!!
I do not have AlfaOBD so I can't check myself, but if it's set as "yes" for you, and you change it to "no" it should remove the tailgate warning lamp. I don't have the option on my window sticker, but it is on my build sheet, and it does not come on when my tailgate is down.