This is a mounting bracket to attach a flashy rear light to your Surly Big Dummy or other Xtracycle cargo bike.Instructions
The Surly Big Dummy doesn't have a great place to mount a flashing rear light. Mounting a light on the seatpost isn't a good spot, since you could be carrying a kid or cargo on the rear rack. Mounting a light on the deck isn't a good option either, as it would get in the way of cargo or the rear grab handle. So, perfect opportunity to come up with something new.
This bracket is designed to hold a Niterider Solas rear light or similar, but could be easily modified.
The part has nut traps for a 5mm hex nut for the clamp and a 4mm hex nut for the flashing light. Use a 5mm socket head cap screw for the clamp. Tighten the 5mm only as much as necessary to hold the clamp in place. If you over-tighten it, you might crack the part.
The Thru-hole in the mount is to run a zip-tie through the mount and around the rack frame for extra security.
I've included solidworks files for your modification. The main file is the master- change that and the clamp and body should automatically update.
Use at your own risk.