make new wiring

I have a lot of problems with my wiring. I can get it running, but i dont trust it to be realibel. Therefore will i make a complete new wiring to my bike.(kz 400 from 1977)
I have read the forum and i will follow the good advises, about being systemical, but where do i start?
I have the workshop manual and the wiring diagram, so i think i will get some wires from an autoelektrican and some connections. But how to start?
(I am from Denmark, so sorry if my spelling is not correct) Thanks from Villy!

I would probably pull the old harness of the bike a lay it out flat. Getting lengths right might be an issue so would try to copy original as close as possible. Bundling and good sheathing is a concern. I use a GM car sheathing for my race bikes harness.

if the big connectors are still good id try to salvage them.make a couple copys of the factory wiring diagram and figure out which wires you actually need factory harnesses are pretty generic to fit several models.take some white out and eliminate the wires you dont need than make a copy of it ,this should simplify things a little.i like to make my wiring harnesses on the bike its easier to get the right lengths that way then you can pull it back off of bike to wrap everything up before final install. goodluck,happy wrenching!