You didn't answer my question. You cut off the end of my question with your quote. I will ask it here is again.
I'm not a DOT lawbook.. can't answer that question, so didn't address it.
a cursory search of the online codified rules didn't turn up any sort of spec for controllers, just rules sayingthe trailer had to have x brake axles if over x weight.. etc.. etc.. age / exemptions.. etc.. etc.
IMHO.. if you had a trailer with a homade controller that worked, and it made the brakes come on.. and for some reason you were inspected.. I'm guessing the inspector wouldn't take yer lil project box apart to scrutinize it. IE.. it either works or don't work.
now.. that's the compliance part. the other reality is the liability part.
say you are tooling down the road.. 7k trailer in tow, got yer 20$ radioshack stop box velcro'd to the dash with some nify leds showing thru so you know you have power and whatnot... hitting brake pedal makes everything work.. hitting panic button makes yer brake lights come on.. yada, yada.. everything cool.. so you are being carefull, doing 5mph UNDER the speed limit, have enough dot grade chain and binders on your load to make any 12 dot cops smile ear to ear.. new tires, all air pressure is correct.. good sunny day.. high visibility, you had a good noghts sleep, and are fully awake. your tow vehicle is beefy and over-ated for the task at hand. all in all 100% perfect towing setup and conditions.. other than the homade 20$ brake controller, you have tripple or quadruple redundancies on everything.. now.. you are on a nice classic old 2 lane road with beautiful woods on either ide and a nice caopy of trees overhead, and beautifully manicured hedges frame each side of the road.. high class community, etc.... now.. the 6yr old girl that lives on that street has tied a rope to a branch in a tree and is playing swing... she's a 6yr old kid so is not paying attention, she's having fun and is hiding at the top of one of the hedges 100% out of site.. and leaps out and swings right out in middle of the road, and her rope comes loose and she lands 6" in front of your truck tire... it happens so fast.. like 500 milliseconds.. and you literally almost can't even process the data your eye has encoded, let alone have your brain tell a muscle to move, to stomp a brake pedal... the signal from your brain to your leg is racing down the nerves about the same time the truck tire runs the kid over fully and mashes her flat. Oh yeah.. her mom can't have any more kids.. so she's the 'special girl', and her rich dad's the one that lives in the mansion at the end of the road, next to the private clubhouse. also.. he's the senior partner in his own law firm that has 2000 lawyers that practice in ever state and 6 other countries. His daily driver car is a 'beater' lotus just so he doesn't 'dirty' any of his 'expensive' cars.
So yeah.. he sues your pants off.... the inks dry on the lawsuit before your vehicle rolls to a stop..
since he's a billionair.. his team of 2000 lawyers hires every pro mechanic, traffic specialist and expert witness that money can buy in order to 'investigate' the accident.
after plenty of red hot poker style investigation.. they find that ho-made brake controller.
AH-HAH .. he couldn't stop his vehicle because he didn't have a 'proper' brake controller..
even though you would have needed a time dialation machine in order to react fast enough to have actually stopped before hitting hte kid that flew out inches in front of the truck, and the fact that no technology known to man would have prevented the truck from hitting her at the time of the accident.. well.. that won't be heard in court. all the jury will hear is that you had a homade controller, and your truck didn't stop before it ran over 'princess'.
pretty much assured to get a landmark jury award. the kind that would make a money-vacume sucking sound that you could hear in a distant galaxy for decades to come... even though sound can't propogate thru a vacume.. etc. your car insurance, which you actually upped to the max, and had a 2m umbrella policy.. just because, well.. that maxes out and so does your homeowners, and that doesn't even cover the coffee the investigators drank during the first day of investigating you. the rest of the award money, which.. likely exceeds all the currency in circulation on the planet has to come out of your backside. in fact. it's so much money, they'd have to clone you 6 billion times, and colonize the moon with your clones, then harvest all their organs, and sell them, just to make the first interest payment... and then......
see where this is going
oh yeah.. the 50$ walmart one wouldn't have stopepd ya either.. but it would probably have some sort of lable on back.. maybee 'ul' or some other test agency... you'd still get sued and loose and be sold into slavery and all.. but..
soundguy