What’s involved can vary drastically from car ro car. Most factory wires are color coded, and if you can get a schematic you’re way ahead of the game. Remove all or most of the wrapping so you can see what’s going where, and spend some time looking at it to get a feel. You may want to give up right about them. They are only wires, concentrate Trinity…..

I use both solid color and striped wire for replacement, and create a new schematic for myself if it gets real complicated.
Now, keep in mind I've never done one as complicated as my '99 benz. I would certainly try to repair only the problem wires. Here is how my past projects usually start out: I'm trying to fix something like A/C or instrument cluster etc. After creating a birds nest of wires I start hacking wires that are not important. (You'd be surprised how many wires I've traced to nowhere.) Those get hacked out and before you know it ½ the mess or more is gone. While rooting around I find bad insulation, bad connectors, bad switches etc, that I repair or replace. Also things that I consider un important get cut as well, not important is a matter of opinion. The end result isn’t as pretty because I don’t wrap it like a mummy in 30lbs of tape, but it’s now easier to work on and trace.
Only once have I completely stripped a vehicle and replaced every wire. It was a big job, but mostly because I’m anal and soldered and heat shrinked every connector vs crimping.