Alright!
Special thanks @Jedadiah for his help an precision on tapping the brake light for the brake controller.
Tap installed on BMC A57
Reinstall
Moment of truth
https://youtu.be/FwbU1IBzUpA
Brake controller installed!
Immediate road test to Canadian tire to buy soap to clean that dirty trailer.
She ride a little bit too low for my taste. I'll try to reduce the tongue weight or I'll install air lift bags. Still trying to figure that part.
TDI/DSG
I did alot of city with few km on the highway. First impressions, the DSG shift perfectly. I thought it would need to be on sport mode but it wasn't required.
You will smoke the tires if you ever try to start from still too quickly.
It was easy to get on the highway, speed of 100kmh/60mph. Transmission even shifted on 6th speed when it feel you don't want to accelerate anymore.
I previously towed this trailer from Canada to Texas and back with a 2015 5speed auto 4.0L 4Runner.
The TDI/DSG struggled less than the 4runner to maintain speed on the highway.
The transmission was always shifting, 5th speed was hard to reach and overdrive was non-existent.
Stability:
This has nothing to do specifically with the GSW, it's common sense, this is not a truck, it's a compact car. I mean, you can feel it's less stable. You will also definitely feel it when you get passed and you will definitely feel the slightest breeze.
I'm aware that my new rig is less forgiving then when I had a 1000lbs heavier truck.
I'm still debating whether or not I will weld/ install an anti sway.
I wouldn't go over 100kmh/60mph with that rig.
Also, even if they are not required in your state/country/province/native reserve trailer brake should be installed when you install a hitch on a small car.
So far, I'm impressed!
I will be monitoring this thread if anybody have question. This forum helped me alot, I'll try my best to help.