I was kind of waiting for someone knowledgable to answer this. I can give you my experience.
I made my own loom for my 1961 GF so the wiring is suited (mostly) to the way I chose to run it. Additionally I have fitted an alternator and electronic ignition.
From the headlamp shell I passed the loom on the RHS of the headstock in through a hole in the headstock. This is a site of high wear as you would expect. I wrapped all of the loom in self amalgamating tape but this is not enough here and I plan to reinforce this here as a winter job. the loom passes between the top two frame tubes.
I then passed it onto the LHS of frame and threaded it through the middle of the head stays.
The loom then passes under the rear head stay bolt under the RHS Frame tube passing to the left of the battery box. Many of my wires lead to the tool box where I put the electronic ignition and coil.
John
