Not sure what you are asking about.
Four main parts to trailer wiring...
1. the wire
2. the truck connector
3. The connections/splices
4. The lights
Aside from light bulb replacement (not the case with LED) Most the issues are with either the truck connector or the connections/splices
Not much you can do about the wire size/quality of the leads coming off the LED lighting fixtures. Because most of them you HAVE yo use the 6" or so flying leads they give you, because the light itself is sealed. And I dont even think the more expensive high quality lights have heavy gauge wire or insulation.
So it all comes down to your splice. So whatever "wire" you choose to run the length of the trailer.....at some point you have splices. And you need your splices to be waterproof. Because even using heavier gauge wire they will eventually corrode and fail.
About the best I have found is Ny-trex butt connectors. They are a heat shrink butt-connector with like a glue/sealant in them. And they work well for repairs, or for new install of lights.
As for the wire....I like the stuff that looks like SO cord.....but made for trailers. Industrial SO cord is fine too.....but the wire colors are wrong for standard trailer wiring. Buying the stuff that e-trailer or several other retailers sell specific for trailers makes wiring east because it is color coded. Just note that the SAE standard (most equipment trailers) is different color coding that RV standard.
Just note that 6-strands is really all you need on a equipment trailer with brakes as most dont have reverse lights. So get 6/14 wire because 7-strand wire is pretty tight fit in some 7-way connectors and also more expensive.
I also dont like using the frame as a ground. If a light fixture has a ground wire....I want it spliced to a ground wire and not a ring terminal and bolted to the frame. Just my preference.
As to the 7-way connector.....you can get the plastic ones you assemble yourself, or you can use a sealed molded one....but at some point it still needs spliced to the trailer wiring. Again, you can either use nytrex connectors or a junction box with studs and ring-terminals on the ends of the wires. I have done it both ways and have had success both ways.
But the wire....you can literally use whatever wire you want......as long as its secure, not rubbing or getting pinched....it is rarely a problem. ITs the connection points. So focus on what you can control
