I'm not really sure how much pre-wiring would be done on them. If it is easy to check and I have the time, I can try to remember to look, no promise. If it turns out being actually IN the tailgate, i probably won't even try, as the newer tailgate trim is a "beach" to remove. Somehting tells me it's not in the gate though, I think it's under the rear trim plate.
To add difficulty in checking what you want to check, if the tailgate is open the compass won't work, it must use a signal from the latch to determine if the gate is opened or not. If the gate is opened it screws up the reading, that's why MB did it this way.