I installed an universal aftermarket wiring harness back before there were nice plug and play options from Painless and American Auto Wire. Since then, I added cooling fans, H4 headlights and a MSD 6AL making the wiring kind of a mess.
Prepping my car for fuel injection, I knew I had to rethink my wiring and build a new harness for the front of the car. I also knew I had to start with an alternator that not only produced sufficient amps at lower RPMs for all of this but also one that produced a clean signal to my battery with minimal RFI. I selected a 105A CS130 as fit all of my stock brackets, was reasonably priced and if I needed a replacement could get one from any local auto parts store. A 91 Chevrolet V3500 diesel turns out to use a V-belted CS130 that happens to have the correct clocking for my application. Everything you need to know about the conversion can be found on Youtube.
You look under the hood of a new car, you will find a bunch of relays centralized in some sort of protective box. This is to isolate sensitive electronics from electrical noise and lower the amperage load on other components. I wanted to duplicate that as close as practical. I bought a premade box which was nice but didn't do what I needed it to do so I ended up scrapping that and laying out my electrical plan on a dry erase board and building it myself. My box is located behind the core support and contains both ground coolant fan relays, both positive triggered high and low beam relays and a ground triggered horn relay. I also left capacity in the box for one more 40A ground triggered relay for a future line lock and 2-3 additional positive triggered, 30A micro relays if I need them. I also needed a ground triggered relay for the fuel pump and one positive triggered relay for the fuel injection computer which are mounted in the trunk and other side of the core support respectively.
This all took a ton of planning, work and time. The planning paid off as everything tested out perfectly the first time and looks much cleaner.