A 2021 updated Trailer hitch & brake controller thread

[HansBimmers]

So by now if you've made it into this phase of e53 ownership (owning a 15-21 year old SAV) then towing may be just for you, but the cost of a genuine BMW system is prohibitive at $1,200+ dollars for almost the same thing you can get for much less, and on these vehicles the cost could easily be twice as much with labor installed as the cost of the entire SAV! Considering my dd X5 is a 216k mile, 2001 3.0 AT, its definitely the case with my tow mule! But I have maintained her well so she is definitely up to the task.

Reality check #1. Using a Curt hitch (cost: around $100 shipped) rated at 5k/6,000 lbs (depending on engine size) can work as it uses heavy duty square tube steel and has beefy welds throughout, but the hitch has a couple caveats:
1) The riv-nut that attaches the longitudinal stabilizer bar and rear subframe is difficult to mount properly without tack welding it in 3 spot to keep it from spinning while tightening it up so it expands/sets properly.

2) Scuff and coat the entire hitch with epoxy bedliner spray twice, which keeps it rust free for a long time overall. From the factory, it is shipped without a package and gets some coating removed around the edges. Its a standard coating which is weak rust control by BMW standards. $5 worth of Bedliner solves this issue.

Reality Check #2
Brake Controller is pretty straightforward, but with one important issue yet to be solved:
1) Clean brake pedal trigger wire: that needs to posted freely on the web and it should be on a sticker and the wire itself- which should located inside the spare tire area and also where the tail light wiring is, to avoid serious injury or death: The exact location and color of wire to signal the brake controller to brake CLEANLY, and the color codes for the 4 flat adaptor installation (brake, turn, tail).
2) I used what was available, which was a brake light wire which due to its BMW bulb checking circuit, makes the trailer brake controller go crazy- sporadic braking on its own, eventually controller calls a short circuit message, and then no brakes on trailer! It was so unruly it caused the vehicle to go into limp mode twice!

3) Right now, the Hopkins brand Impulse model works perfectly without the headlights on, so I guess its not checking or throwing random testing voltage thru the circuit while the tail light markers are not lit. It's soft upscaling of brakes keeps the braking from being jerky, but there is a small release jerk upon releasing the brake pedal.
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4) in conclusion, BMW and these brake controller manufacturers should have this type of thing standardized for the consumer since American consumers have been towing tons of trailers for 60+ years, and buying a trailer of sorts on a whim and safely towing it home in a matter of hours is has been considered 'the norm' for most Americans, so it should be an embarrassment and their legal fault to these manufacturers to not have the ability to readily identify the necessary wiring and safely install a brake controller without a degree in electric engineering.
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I would like to complete this thread and make it a DIY article for e53 owners, any input would be appreciated!