I have used "painless wiring" kits with good success. They are not too expensive and they are labeled and come with the diagrams. If you can follow a line and read they are easy to install. Just contact them by phone and advise what kind of car and engine you are using, steering column, power windows, yes/no etc.... And they will fix you up.
I just did a 51 merc with a rebel wiring kit. It was very nice. Had a question and called the guy, very helpfull. The wires are labeled all the way to the end of them, make it very easy.