Alright then. Back to basics.
Power for the fuse box is supplied by the white wire with red stripe from the battery. It powers up the 30A fuse. Check for power at the white /red wire at the fuse box
The downstream side of the 30A fuse is a white wire with a black stripe and it powers the Main Switch. Check for power at the white/black wire at the fuse box. That confirms power going through the fuse.
The white/black wire powers up the Main switch. Check for power to the white/black wire at the main switch. That confirms power to the Main.
The white wire at the main switch is the power feed to the ignition switch, so check for power of the white wire at the Main switch. That confirms power through the Main switch.
Up at the ignition switch, power should now be coming through the white wire. Check for power of the white wire at the ignition switch. That confirms power at the ignition switch.
With the ignition switch on, power should be provided to the brown wire. Check for power on the Brown wire. The brown wire now feeds most of the circuits to run the electrics.
So what I've shown here is the "flow " of power from the battery to most of the electrics that run the bike. Obviously, if you have power on the brown wire at the ignition switch, all of the previous "checks" are redundant. If no power at the brown wire, then you have a "check list" to troubleshoot with.
Hope this helps. I know wiring diagrams can be a lot for some to work through and it's why I advise everyone to take an electronic copy of the wiring diagram to your local print shop and have them blow up the diagram to 11" x 17" and then laminate it. You can then mark up the laminated copy with a dry erasable marker and make a flow path of a circuit you want to follow. Once you're finished, you can clean off the marker and put your diagram away or hang it on the wall of your garage as "Mechanics Art". it won't be long and you'll become an expert with wiring diagrams. I've had lots of practice especially with my previously owned Porsche928. That one is a nightmare compared to the KZ1300 wiring diagram.
Let us know how you're making out please.
KB