Check out back issues of Scale Auto Enthusiast (now Scale Auto, Kalmbach publishing) I know they ran several articles on wiring and plumbing.
If it is for a contest, use reference, if it is just for your own enjoyment get under your car, look, and wing it!
As always use Google and ask for what you want, do not forget model sites as well.
Several after market companies make kits and they have instructions/tips on how to, again an issue of Scale Auto or Model Car magazines can load you up on companies and reference.
I model F-1 and Indy Cars, I use The Anatomy of a Formula One Race Car for reference as well as pictures I took at the Museum in Indianapolis and the Henry Ford in Detroit.
And teams use different methods to wire and plumb so if you are doing a specific car, go to their web site and see if they offer assistance.
Good Luck!