oh my... The thought of rewiring a car just sounds like a ludacris idea. no not the rapper. ;-)
I'm an electrical engineering student. And if you were to try to re-wire your car... I dont think it would be possible( unless you've re-wired about 20 cars).
The design that goes into complex electrical systems is something I cant even grasp yet... If you get lazy and just hook something up to 12V because you cant figure out where it should go you could burn a lot things up REAL QUICK. All you'll see is a puff of smoke by the time you realize something isnt right and that electrical component will already be toast.(then you have to find the exact replacement component. and good luck with that.)
I'm just telling you this so maybe you'll reconsider this idea.
If you are just dying to do this, I would start by cleaning electrical connectors and contacts. replace plugs that are gummed up, ...etc. Plug wires back in that got pulled out, w/e.
The chances that your wires are bad is one in a million. the plastic sleeve around them may have dirt on them(which you could clean up to make them look nice) but I dont think plastic even degrades, so they are still protecting your wires as they did out of the factory.
but yeah, clean wires/connectors, if you find an exsposed wire, cut it out and splice in new wire. but thats as far as you should probably go.
Just as a heads up as to what you want to get into, these are some equations that you would HAVE to use:
Kirchoff's current law (sum of the currents in a closed loop=zero)
Kirchoff's voltage law (sum of the voltages in a closed loop=zero)
And if you cant use these then its hopeless. Hope this helps.