Does anyone know where I could order an aux brake light to mount onto the back of my bike rack? Something that will connect into the 4 prong pony-tail. The tail lights and 3rd brake light get pretty well covered when there are a few bikes on there and some extra visibilty for the people behind me would be nice and it would reduce the risk or getting the bikes all smashed up in a rear end.

Any auto parts, tsc, walmart, harbor frieght, northern tool, would have what you need to make one. If it were me I would splurge and get the LED marine lights. How you want to mount it depends on the rack that you have.