are all the lights in that assy. going out? just wandering, sounds like a bulb prob. if just on one bulb i.e. brake or turn, i know the turn bulb is dual for marker light and then for turn, i cant remember if brake light also dual for marker? then you have the back up(single fill) and the outer marker(single fill) does the prob. happen all the time, if it is all lights inop? i.e. in reverse do all lights work while applying brakes ? you might be able to single it out if you think about what is working and when or when not it's doing so