Yes, the question of wiring has arisen. I was asked about the wiring on my 1923 touring, so I supplied this old picture with the caution that it's not correct. It's pretty much as I received the car except for the speaker wire I installed for my bike speedometer.
The guys who "did" this car used Phillips screws in the body, and I assume they were just as careful with the wiring.
Here it is today as I'm in the midst of reinstalling the engine. Apparently the wiring harnesses available at the time (about 16 years ago, I think) weren't terribly correct either. Note the black/red magneto wire which should be red, and the tacky plastic insulator. I don't know why the mag wire has a terminal with such a huge hole.
After all that, now we get to the questions. Is there a correct reference that shows what goes where? Figure 39 in the service manual shows where the clips go, but what are the little holes in the firewall for? Do they have anything to do with wiring? If not, what's their purpose?
The wire retaining clip that is secured by the hood rod on my '23 had the wiring harness above the rod. There was also a clip on one of the body bolts coming down towards the steering column.
I did find differences in vintage wiring diagrams such as the use of brown and grey wires used for the headlights which are not used in the modern harnesses. They use black with red or green tracers. Also the switch diagrams in old writings had two different locations.
The low cowl '23 has the loom wires at the base of the terminal strip. The tiny hole down below is for the horn wire. Mine has another wire there, for the stop light switch at the pedal.