You might want to follow Bob's advice concerning the connectors. All you have to do is take it off and you can also unclip the connector to expose the metal teeth fittings. You can clean them with a light sand paper and pinch them with some pliers so they get a better connection. Also while your at it, go ahead and use the sand paper to sand lightly on the copper ring where the bulb holder rests on when screwed onto. There will sometimes be loss of elec. contact between the bulb holder and copper ring (ring being on the circuit board) from a deposit build up. This is a very simple procedure and solved my brake and back-up light problems after 3 years. You might want to check them out once and awhile to make sure they're still working from time to time. Take care, and hope this helps!
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Michael 'Street'... one AZ '85 244DL 185K miles