Originally Posted by
unterhausen
I took the op to mean getting from the fork to the main triangle.
When I made my fork, I drilled holes in the fork blade and steerer to get the wire through. Sometimes there are vent holes in these same locations, but unless there is a vent hole in the steerer I don't know how you would know that the blade was drilled. Or get the wire through for that matter. Would be somewhat tricky to drill after the fact.
Indeed. Yeah. You'd definitely need to be able to see up inside the steerer from the bottom of the crown to even tee if there is a hole where the legs meet.
The feed wire from the hub would have to go directly to the light, from the bottom side of the fork crown. This would minimize flex in the wire, making it a moreorless fixed installation. Then a second & more easily replaced wire from the light to whatever routing to the rear tail light.
Going from internal to the steerer to internal to the frame would require a hole from the steerer to the inside of the head tube. (As I gathered from the op) The amount of wire flex there would be insane. If the wire lasted one ride, I'd be surprised. I would not recommend drilling a hole in the steerer to let the wire out so that it could be routed down the inside of the downtube.
A gas pipe Opafiets I rode in the Netherlands had a hole drilled in the down tube a few inches from the lower head tube lug for internal dynamo wire routing, but the wire was broken at the hole & never replaced. I suspect all internal routing would suffer the same fate.