This is one of two bikes that I considered my wiring to be permanent. Note, no rear rack, sometimes I have a rack on that bike and sometimes not. I built up the bike in spring 2017 and finished the wiring in spring 2018.
Took the photo about three weeks ago, lake behind it was still frozen. I typically have a flashing battery taillight on bikes, here I mounted a battery light on the seatstay mount for the rack.
Photo below is a year and a half old, I had a rack on the bike at that time. Spaninga Pixio (spell?) taillight with guard on fender, wiring is glued inside the fender.
Older photo, bottom bracket area. The wire that I glued under the fender was a poor choice on my part, it is a fairly heavy two conductor wire, one side is red. I say it was a poor choice because it was stiff enough that it was hard to glue it in place. I drilled a hole in the fender and the wire exits the fender at that hole, which you can see because one side of the wire is red. I wanted disconnects in the wire here in case I needed to disconnect something later, used 2.8mm spade connectors as my disconnect there. From there the wire goes under the bottom bracket and up underneath the downtube. That wire under the downtube is two wires, twisted together, I think it is about 18 or 20 gauge. You can see the twisted pair of wires under the downtube.
Year and a half old photo, Luxos U headlamp. I custom bent the bracket for the lamp, but there are similar B&M brackets available. I needed a longer bolt for the fork crown than was readily available at the hardware store, used threaded rod instead. You can see the wire under the downtube is two separate wires, twisted together, zip tied to downtube.
If you are confused by the brake, yes there is a disc brake on the back wheel, rim brake on the front, travel agent on the front brake to convert cable pull to normal road brake lever pull ratio.
I used the same twisted wire to the hub from the light, zip tied to the fork.
I mentioned earlier in this thread that I usually use bolt on skewers on dynohub wheels, you can see that in the above photo.
I mentioned earlier in this thread that one of my other bikes stopped having temporary wiring, now has permanent wiring, when I get photos of that I will post them. I did a much better job of gluing the wire under the fender on my second "permanent" wiring job. And I took photos of the gluing process.