Well you have a couple of choices. There are LED's that will run happily on 12 -14 volts direct and come in the usual variety of colors but they may be hard to find unless you have access to an electronics wholesaler. Might find some on E-Bay.
Run of the mill LED's will require a series current limiting resistor varying from about 470 ohms to 1000 ohms depending on the LED's characteristics and how bright you want it.
I see by your profile that you are in San Diego and I know there are several hobby / wholesale electronics outlets in town but I am sorry I don't know their names or locations. Was in your town a couple of years ago with a resident electronics type who was driving me around but we went to at least 6 shops that should be able to help you.
I would not rely on the likes of Circuit City or Radio Shack.
Hope this helps
John Tones "Penta"
Sidney, BC
