The board LED market has exploded in recent years, especially in the auto and motorcycle lines with custom boards fitting drop-in applications for popular makes and models. A search for "led" and "board" will inundate your results. Companies like http://www.superbrightleds.com are profiting from online prototyping and inexpensive manufacturing to offer a wide variety of product, including simple "plug and play" LED boards with pigtails in common automotive bases that will fit behind tail light lenses.