Re: Wiring inside trailer ?????
often what is hung up is a splice in the middle for the running lights. And speaking of which, that is a major failure point at the splice, so you are better off running a dedicated wire to the running light rather than splice mid-stream. Plus splicing and fishing it out of the hole is a pain.
I rewired one recently and couldn't get the old wires to serve to pull through the new (they broke midstream), and I didn't have an electrician's fishing wire, so I improvised by pushing a 25' tape measure through. Then you tape a string and reel it back; then you use the string to pull the wire. It worked great and I was right proud of figuring this out until disaster struck. See, I had the tape measure small end hooked over the end of the beam, and set the big end in the opening of the trailer beam. Well it came unlocked and my tape measure shot about 4' up into the trailer! Couldn't pull it through, couldn't push it back so I had to build a coathanger on a pole device to retrieve it!
So watch the spring-loaded device; learn from my error.
A plumber's snake would work, too. Also bungee-joined tent poles.