On my 01 I basically started with the connector printouts that I got from ALLDATA. Then go through and find similiar circuits as GM doubled up in many areas of them. The nice part is everything has a plug underneath the fuse panel and unhooks. Many of the colors are the same for each type of circuit(red for hot all the time, orange for hot when the key is on and so on). I just took the connector diagrams and went through after isolating and narowing them down and one by hooked them into the fuse panel and got that part out of the way. Then I took and went through and hooked in the control circuits like A/C and guages and then hooked up the throttle pedal. Once you get down to it and get it sorted out(make lots of notes on paper about which wires to cut out and which are duplictaes that can be narrowed down) it isn't that hard.
Heres a few pics of mine while I was doing it. I was lucky and found enough of the discontinued terminals at my local dealer to integrate it into my stock fuse panel. Also a packard crimping tool is a must have if you need to add in any wires to the factory plugs.
As you can see everything comes together in a central point to make your connections all in one area. You have a main budle that goes to the engine, another bundle up to the ECM and a pigtail off for the TCM, and everything comes back to the central point at the underhood fuse panel.