the modern stumpy
Above and below my solution to mounting the light. I didn't want to use the tab on the rack because it placed the light too far out over the wheel, and mostly looked goofy.
This is a bracket that was left over from some Italian shelving that I installed for a job. It was threaded M6 in both directions and I figured it would have a bike use one day, and viola! I ended up drilling out the threads in the top bolt so that I could get it tighter to the rack. As you can see here, the wiring is a little funky and those tail light stub outs need to be fixed but I was anxious to try it and threw aesthetics to the wind.