I completely rewired my system last year. My plan was to use the original wire to pull the new wire up the rear cap. Didn't work out so well. The original was taped in place and I couldn't get it out.
To get the new wire in I used a snake getting into the cap via the tail light, corner height light and then to center of the cap thru the center height lights. wasn't difficult but took a bit of time to get the end of the snake in the are of the lights. I also ran a pull string incase I ever need to do it again.
I did try using the original wire but was getting some picture distortion noise from some where so I replaced the video wire with coax rather than unshielded copper.
Good luck. Also got the camera and monitor from a Hong Kong internet retailer for less than $100. Color system with an LED monitor.