Personally I prefer the OEM harness. It has the wires for a trailer brake if and when I need one.
It also ties directly into the battery so I don't have to worry about overloading a circuit.
As far as trailers go, here is what I did.
I found a camper sitting in someones yard that was falling apart. I inquired about it and the guy said I could just have it, if I could "get that eye sore out of my yard". He did have a title to it.
Got a trip permit for it, towed it home then stripped it down to the bare frame.
I burnt the wood from it. Recycled all the aluminum, stainless and copper. Which paid for the parts I had to take to the dump. Cut down the metal horizontal side braces(see how the rear is wider) so it was not quite as wide up front, then put 2x6s on the rest to make a bed. Used some 2x4 and Ply/wafer board to make the sides.
Here is the result. 5' X 12' (inside measurements) trailer for just under $500 and it has trailer brakes, but I have never used or needed them.
As you can see after many years(10+) of sitting outside it is due a new set of boards in and out. The first time around I did not use treated wood, so I'm happy with how long they lasted.
This thing can handle 2K of green fir fire wood with ease.
