Excel and Visio
I used both Excel and Visio for my electrical schematics. Excel was great for tracking the wire size, color, length, description, pins/sockets/terminals (and their respective part numbers). I used Visio for the actual schematics. Visio isn't the easiest software to learn but there are a ton of examples on YouTube. You don't need the expensive version. You just make the various components (switches, relays, etc.) via the lines/arcs/etc. in the software and group them together to make a component. I had file that was nothing but the symbols I made. That way I'd just copy/paste them in the various files as needed. If I need a new symbol, I make it in my "Symbols" file and then copy/paste it into the new schematic.
I decided to make a schematic for every "system" on the aircraft (Pitot heat, Nav/Strobe/Landing lights, transponder, etc.). Each system was on it's own page. The wire code I used to label the wires was based on what page it was shown on in the schematics, and the wire number was based on that individual wire on the page. For example, if I see a wire with the label "(07-32)" on it, I know that I can find information on that wire on page 7 of my schematic, and it's labeled as wire "07-32" on that page. The "32" just denotes that it's the "32nd" wire on that page (starting with wire "01"). I included these wire codes in my Excel file too.
As you can imagine, the same wire is sometimes are used for multiple systems. Not a problem. If I need a wire for a particular system, it gets a "code". If I need that same wire later on for some other system, I just use that same code on the new schematic. For example, if I see wire (07-32) while I'm on page 11, I can flip back to page 7 to see what that wire is used for.
Another nice thing about both the Excel and Visio files is I would print them and then highlight the finished wires with a yellow highlighter as I installed them. Both on the Excel row and the Visio schematic. You'r not done until you fill up the pages with yellow...
Take lot's of pictures. You'll need them later. I put wire labels at each end of the wire (unless it was a really short wire where I'd only use one label), and a label in each "bay" it passed through (so that if I was working with only one cover removed, I could figure out what that wire did without having to go dig through the entire harness to figure it out).
After I completed a system, I would test it and make sure it worked properly before moving onto another system. Less troubleshooting if there's a problem.
You can also use this for schematics of other systems too such as brake lines, pitot/static/AoA plumbing, etc.
I hope this helps.
Jeff