Rewiring a car: some ideas
I've run across two pieces of information lately on totally replacing the wiring on a vehicle.
The first was posted up on Make: Online a few days ago and is about a gentleman who rewired his '69 GTO sorta old school, by using structured wiring similar to they way you would wire up a building. THe articles on this are at Make:More On The IPod-Controlled GTO and also here at Jalopnik: Electronics Whiz Controls ‘69 Pontiac GTO With iPod Touch.
The second place I've found information is at isis, which is selling a more sophisticated can bus based rewiring solution. Their site is here.
It's interesting to see the different methods you can use to accomplish the same thing.