In my searching for how to route wires for a dynamo lighting system, I never found a specific thread for running dynamo wires through a fender -- only references. This is how I did it. As always, I hope others will find this useful.

The bike is a very early Schwinn mountain bike frame that I have been building up as a fancy grocery bike. The dynamo/generator is a bottom bracket mounted unit that is essentially a 6v3w bottle generator stuffed inside a yoke mounted drum that rides against the rear tire tread. The rear light is an old fender mounted French PYB Generator light with a Compas Cycles red LED replacement with an incorporated standlight. The aluminum fenders are from Velo Orange.

The key to routing the wire through the fender is the rolled edge. In the case of these fenders, this rolled edge creates a tube large enough to pull a length of 20 gauge stranded wire through. Unfortunately, I neglected to take pictures of parts of this process.

Using 20 gauge stranded wire, I stripped the housing off the first 3 inches. This bare copper will protrude out of the seam of the rolled edge, allowing you to pull the rest of the wire through the fender with a pliers. After deciding where the wire was to enter the rolled edge of the fender, I used an awl and a flathead screwdriver to carefully open the seam enough to push the wire into the rolled edge. Using a pliers on the exposed 3" of bare copper, I pulled the wire through the fender to where the light will be mounted. At this spot I opened the seam enough to pull the wire out of the rolled edge.





Pulling the wire should be fairly easy on a new, clean fender. As I discovered late in the game, mine have a few years of dirt and mud built up inside the rolled edge. Before starting, this will need to be cleaned out. A spray bottle of soapy water and a bent paperclip worked quite well to dig out the mud. I suspect, in the end, the soapy water made pulling the wire easier, so it is recommended to spray the inside of new clean fender anyway.

To finish off where the wire enters and exits the fender, I used 1/8" aluminum pop rivets with a reenforcing washer on the inside.




The center pin of the pop rivet can be pushed out by filing away the back side of the rivet and carefully tapping out the pin with a drift punch or an awl. To file away the back of the rivel, I used a carbide grinding bit for a die grinder that was chucked into a drill run at a medium speed and a steady hand.

On the rear light, I considered trying to run the wire directly into the light housing. However, due to how close my fender is to the wheel, I was concerned that the extra length of wire might eventually droop into the tire and be worn away.

Eventually I will clean up the mess of wire connectors behind the cranks. My bottom bracket generator did not come with a complete mounting bracket, so I might incorporate a small metal container into whatever I fabricate to replace the fender washer.