Question about the hitch harness

[Der Pfaelzer]

Good morning,
We just bought a 2006 X3 E83 1 1/2 weeks ago. It has 87k miles and is in great shape. It was from a dealer and it took two weeks to fix the rear wheel speed sensor and the rear axle shaft. It had to be replaced because it showed a few warning lights.
We like the X3 because it is small enough to use it as a daily driver and it is big enough to tow a boat.
Currently the car does not have a hitch, but I would like to install the following one:

Part# ES#185398 at the ECS Tuning website.

If I copy the link in here, it redirects it to some weird page, sorry about that!

I believe that thread is the right one about installing it:

https://xoutpost.com/bmw-sav-forums/...h-2006-x3.html

It comes with the wire harness, the round connector and the adapter for the 4pin connector.
I was reading that you need to plug in the harness into the white box that comes with it and also into a connector in the back of the passenger side.
So, now to my questions:
- what is the white box for ?
- what signals/information is send between the trailer and the car ? Is it just the lights and turn signals or does the car now that a trailer is attached and it changes the way it
is adapting the xdrive and the braking ?
- I tried to take a picture of the connector that I think is the right one. Could someone verify that it is the right connector?

Thank you so much for your time and help!

Pfalezer

http://i63.tinypic.com/2jb8m7r.jpg