After the test ride, I was motivated to get the lights and horn wired up and get out on the road. Fortunately, I saved the original wire harness and was able to re-use the connectors and many of the original wires.
First, I determined what I wanted each of the switches to do for the 12V components. I wanted the lights to be operable when the key switch is on, regardless of the position of the run switch. That way, the run switch could serve as an emergency kill switch for the drive system without killing the lights. Also, I wanted everything to be inoperable with the key switch off, so I could be confident when I removed the key that there was no drain on the battery pack.
Or virtually no drain, to be precise. The DC/DC converter would draw 0.7 W to sustain the unswitched output. But it would take months to drain the battery with such a small draw, and I could pull the fuse to the DC/DC converter if I wanted to reduce the load to zero for long-term storage.
I wanted the flashers to function using the original switch. Same with the brake lights and horn. I wanted the headlight and tail light to turn on when I placed the headlight switch in the first detent (the position originally for running lights). This would be for daytime operation. I wanted the pilot lights and speedometer backlighting to illuminate with the headlight switch in the second detent (the position originally for headlights). This would be for night operation.
I wanted the high-low beam selector and the high beam flash switch to operate as normal. I had no use for the electric starter switch, and I left the ammeter and ammeter backlighting disconnected as well.
I opened up the wiring harness and separated the wires as much as possible so I could look over the whole thing.
I studied the wiring diagram in the shop manual, looking back and forth from the diagram to the wire harness to figure out what each (or at least most) of the wires and connectors were for. The colors of the wires were very handy in understanding the wire harness.
Then I drew my 12V diagram, using some information from the original diagram, but mostly just making sure that when I turned on a switch, it would put 12V where I wanted it. In most cases this was intuitive, although I did not find the wiring of the flashers so obvious. In that case, I just did what the manufacturer did.
Also, I discovered that during the De-ICE process I had accidentally gotten rid of the flasher relay. I did not know what it was when I stripped it off the bike and shipped away the parts. Fortunately, I found a replacement flasher with the same terminal configuration online for less than $2.
I cut away the wires I did not need, such as the battery, ignition, starter, and alternator wires. Many of the remaining wires were already going to the right connector for my design, so I left those in place. And some needed to be cut and spliced in a way that would support my design.
When I got them all attached, I flipped each switch, one by one. I could hardly believe that my spaghetti mess actually worked the way I intended! In reality, it is not so utterly complex, but the large number of interconnected wires can make it feel daunting.
I gathered the mess into a bundle and zip-tied the wires onto the frame. I would come back later to shroud the wire bundle to protect it better.