I agree with MGTR, if your cables are pulling out as you say then you are doing something wrong or the cables are too short. When you plug into the MH the flap should come back down and hold the cable in as designed. The same thing with the end on the car. They both should be a snug fit. I don't use the coiled cables, I use the straight cable that runs thru the Tow
Bar.
Now as far as 6wire to 4 wire, they have adapters for that. But because you have replaced the ends no big deal. Just make sure as someone else has said, don't do the mirror image thing. When all else fails, plug in the MH side then get your multimeter out and test the car side wire by wire before putting the end on it. Make sure you have pencil and paper to draw circles and input the color wire and what its for.
As far as the cable I would tie wrap it to the Tow Bar and make sure there is enough slack on both ends for maximum turns in either direction.