Most bike racks come with pre-drilled holes for mounting lights. If your rack does not have these holes, you can use zip ties to attach the lights to the rack. First, position the light where you want it on the rack and mark the spot with a pencil. Then, make a small hole in the marked spot large enough to fit the end of the zip tie through. Next, thread the zip tie through the hole and around the light, then pull tight and trim any excess length. Finally, repeat this process for each light you want to mount on the rack.