There should be a plastic cable holder that came with it. (You can find them in the electrical section of Aviation Depot). Others have told me to place it in there and just screw it to the underside of the wing where the fairing goes. I might also add some glue to keep it in the holder.
One thing for sure, you want to put it away from the engine and exhaust. Best place I've gleaned from others is somewhere on the wing. I plan to do mine on the first inpection panel.