Assuming you are in the USA, there is one set of lights in the rear that are not used here.

Pull all the others and check the bulbs and also look for corrosion on the connections.

dont forget the bad bulb could be the left tail light in "foglight" mode too.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)