new years eve:

I noticed my right rear break light the bulb to the inside will only light

when I don't have my driving lights or head lights on . But the second blub

still works right if the lights are on or not , not a burned out bulb already

checked this . Idea's

richard

Check and clean contact end of bulb and inside of socket where bulb sets. I'd replace the bulb anyway, you're out a buck. Sounds like a corrosion issue, most likely with the ground side of things.