I assume its the fuse or the bulb, where can i buy the bulbs? WILL AUTOZONE or someone local CARRY them or do I need to go to the dealer?

My third brake light is on the trunk lid

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1999 SL 500 Sport 42K miles - the head turner
2005 Acura TL - my reliable one, love the bluetooth
2002 Mitsu Montero Sport (Wifes)
2001 BMW 540i - bye bye to a new home
http://new.photos.yahoo.com/e2venu/album/576460762320707219