You could just go to a Radio Shack or any auto parts store and pick up a 12 volt light like this, or a clear one. They kind of snap into place once you drill a hole for it. Only costs a couple of dollars.
hey jay i bought these on ebay awhile back. just some white led lights and bought a switch from radio shack and i spliced the wires from the light that was on the original fender where the plate mounted up to. where it suppose to shine on ur plate. stock wiring. heres some pic's for ya to give u an idea how it looks. although i dont plan on using this under tray since i have the carbon oil box coming soon.