Don't know if this helps
I got a big piece of chipboard and with an artline wrote where all the components go. I then put nails in the wood so the wiring would not move. I then went about fixing the harness and getting rid of any unwanted bits. I did have the wiring diagram as a guide. I was pretty confident of my work everything looked good so I insulated it all whilst on the board. Once in the car I hooked up the battery and where I could tested with a 12 volt test light. Withthe guages I just hooked them up and watched to see they went biserk. Everything was cool. If you start form scratch with wiring and are thorough and logical about it ther isn't much to it. It's when things don't go right and you have to find the problem thats when the real problems start.