JUST MY 02
Trailer lights absolutely suck.I own 5 trailers, 4 for work and 1 for the boat. Whenever I buy a new trailer i tell them not to wire it. When I get it home i wire the trailer myself. What you want to do is get 12-3 insulated trailer wire. This is the kind that has the rubber casing around all three wires. DO NOT USE the typical yellow and brown wires which are always exposed. Buy an outdoor waterproof junction box, a 4 or 6 pole trailer plug(which ever you use) and solder. Mount the box in the front of the trailer. Bring the wire that will be the trailer plug out the front and two others out the back. Run one piece down the port side to the rear of the trailer and one down the starboard side. Solder the connections for the lights in the back and use the white wire for a ground on the back of the light. Solder all the connections in the junction box and wrap in tape. If you have lights on the sides of the trailers run a separate feed for those. Do not tap into the main brake/directional feed for side running lights. Put the new plug on the truck side and your done. This way there is only one connection box for all the lights. Also , silicone the ends by the lights where you have to cut the rubber insulation so water won't get inside when you back it in the water. This may sound a little overkill ,but i'm a little anal and it works.