This is an older post, so the info might not be needed any more, but when i had to fish wires through the rails on my old pontoon boat I would tie a small piece of foam to a long piece of light string like yarn, tie the other end of the yarn to some twine, then use a shop vac to suck the piece of foam from one hole in the rail to the next. the foam drags the yarn with it, then you can use the yarn to pull the stronger twine through, then use that to pull the wires. Just be careful not to suck the string completely through. lol. I left the loose end connected to the spool and watched for it to pull tight. Might not work for really long runs, but it sure does help get the wire fished around curves and corners.