My 72 harness has 1 or 2 quirks with it like the tributary branching off before passing through the frame grommet instead of behind it like I'd planned. Also there are some tight spots where some of the wires could have been 1/2" longer so they weren't practically trying to pull themselves off their terminals. Although the following may be pretty basic it may help avoid some of these annoyances.
Are you using an old harness as a doner or are you starting with new wire or both? If you use an old harness you can use the coded wires for the same components as in the standard wiring diagram. If you are using a doner harness start by hanging it to the rafters and stripping all the tape off. A razor knife is handy.
Plan where all your components will be mounted. (I concentrated most my electronics at the battery box on my 72)
Plan where your junctions will go. Norton uses the headlight and under the tank as main junction spots so you can disconnect wiring when removing parts for repairs etc.
Bolt all electrical components in position (lights, switches, ignition stuff etc., everything) Tape the barrel (gang) connectors to the frame or where you will be using them. Think of the gang connectors as components like everything else as it's easy to forget them.
With all components fixed in their positions you can start stringing wires. A wiring harness resembles our spinal cord with the bulk of nerves traveling along the backbone. Tributaries branch off and they fork out to the different extremities. Run the long wires first. As you add wires, tape them together with a single wrap of tape when they get close enough to any other wires but leave the ends long. Velcro strips would work better than tape for this when building up the loom as you can more easily open it up and add a wire as you go and you can more easily slide the wires in the loom to remove any slack. As you progress you may find you may want to change how a wire is routed. Main tributaries should follow along frame rails or other components and remain as hidden as possible. By taking the shortest path you may find the wiring itself may hinder the removal of certain parts at a latter date. Before crimping or soldering the ends make sure the run of wire is a little long as you will loose a bit of length when you start taping it all up. You are better to have the wiring a little too long rather than too short where it would pull out from a connection because it barely reaches it. Before soldering or crimping use lots of tape or velcro strips on the harness every 3-4 inches and at branch off points keeping the bundle of wires super tight so the points where tributaries branch off and the wire lengths remain accurately positioned. When it's all tight and in place trim off long ends, crimp/solder and tape it up. It will be easier to remove the harness to tape it up.
I assume you would be using the stock switch clusters on the handle bars. They connect to the main junction block under the tank so you could wire dummy circuits from there to the signals using black wires just taped to the harness and strip them out later.
