They are color coded and pinned, if you have the GM wire diagrams you can trace everything. Most of that stuff is all over the internet and would be easier to search than myself trying to explain it.
You will need a different computer (gen 1 vortec stuff is COMPLETELY different).
I've done a few retro swaps for myself and others, and in the end (especially if doing it for a living) the splice and trace method on a factory harness is very time consuming (and not cost effective for myself).
Since you are starting with a harness that's been hacked already (thanks to the junkyard, very typical) you would be better off in my opinion to either grab another complete harness from the junk yard and pull it yourself,,,,or get a ready made plug and play harness and eliminate all the hassle.
Since you don't have a computer, and your harness is hacked, Frankly I'd go the custom premade harness route because most places will also supply the computer already custom tuned that eliminates all the stuff you don't need.
I've been using Howell for years without a complaint, but there are many others if you want to shop around. I find Howell competetive on prices, and their tech support is excellent. A computer and harness ready to go, along with new 02's, new MAF, only sets me back $800,,,,and these are sensors you should be replacing anyway while doing the swap if you want a solid trouble free rig ready to go thousands of miles.
Personally since your harness is hacked up, and if you are determined to go through with it rather than start with a better harness, I wouldn't recommend splicing into that and trying to extend the wires unless you are extremely competent in your soldering skills. It's a recipe for troubles later down the road, and can cause higher than normal resistance. Your best bet is to remove those cut wires completely from beginning to end and start fresh with proper color coded/gauge wires to eliminate any possible trouble years down the road.
It's going to require specific wire connectors and weather packs, and gets really involved (some of them have to be sourced and are not available local), and will nickle and dime you to death if you do this properly.
Plenty of hack jobs out there though where people try to do this as cheap as possible. I've seen some stuff that is down right scary
I wouldn't even touch.
Goodluck with it, it's definately an experience you'll remember
