if you need lamp cord for marker lights the hardware store sells it for something like 30 cents a foot. I found it best to run it from the tongue running back rather then from the tail lights back forward. this makes the tail light connections easier to make waterproof. the one thing to watch for is test your left and right blinkers before wrapping it all up in case you got the yellow and green wires from the plug mixed up for the wrong side. another tip is use the old wires to pull the new wires through the tongue. it sounds obvious but sometimes its easy to forget and just pull the wires out before realizing what you just did lol.
also I mount my marker lights on the tongue forward of the yoke so it stays out of the water when launching, those damn marker lights always seam to go bad after getting wet.
one last tip is I would use all LED marker and tail lights and for the tail lights, smear a big blob of silicone on the wires where they go into the light. that spot seams to never be sealed well and I find it almost always leak and let water into them.
if you want even more extra abrasion protection you can by a roll of wire loom to cover your wires like this:
http://www.ebay.com/itm/50-Feet-FT-1...item43dc844952
you can never say never but after doing all this I think you would never have to touch your trailer lights or wiring again for as long as you own the boat.