Jersey guy,
to me is looks like one that would come off the bottom/side of a door. Like a back door, or side door. Not sure...but it is worth a check.
1) Go to the back of the H3!
2) Open the door!
3) Look to the lower door frame - right next to the right (as your looking at the back of the truck) tail light.
3) Take the plug you found in the driveway.
4) Stick it in there.
5) Close door!
6) Laugh - because you solved the mystery!
Not sure if I am right...but I hope so!
