Try the position above that, or splice that one.
There's a few things going on:
- Tesla is continuing to update the software, which has (several times) resulted in changes in 12v behavior at various places.
- Tesla is continuing to update the physical vehicle, which has resulted in changes, including wiring harness changes. For older production, both positions did not have wires. (In fact, yours is the first I've heard of.)
- The original video by /u/ingineerix that showed clear images of the bare VCLEFT has been lost; unfortunately, that was our best source of documentation for that connector. My best recollection is that those two positions were labeled "SUNROOF" and "TRAILER".
- /u/ingineerix tested both of those late last year, and at the time, they were safe to draw from and behaved as you would expect a conventional "switched" source to behave.
More recently, /u/travisllado has posted using the upper contact on that same connector to provide switched 12v to his aftermarket audio upgrade. (See picture at the end of this post, taken from his gallery at imgur.com/gallery/WtteZMn ).
So, my guess is that Tesla has populated the red-wire-position in the harness, perhaps to lead toward a hidden other end trailer connector somewhere in the tail area, perhaps for something else. Likely that you could tap that and see how it's being switched; also likely that you could use the other position and test to see how they're switching that. Personally, though, I wouldn't disconnect anything without knowing what it was -- tapping it is more reasonable IMO.
None of this is done from official documentation or recommended practice -- we're all just figuring out what seems to work, and then adjusting when an update changes it. Welcome to the underground.
from /u/travisllado's gallery: