It was explaned to me as this way, if it is installed buy the manufactor it must be present and working, if it is a add on safety impacting item it must be working, if not must be removed, or repaired. You can call the DMV Enforcment office they can be more specific. I dont have the number, but will try to get it monday.
I ask my next-door-neighbor the NC state trooper and his answer was this: It is required to be opperational if visible, however, if it is obstructed by a cap, camper shell, trailer, etc. then it is not required.
He said that you might want to disconnect the light though, just to "keep bored cops off your back" so the glow is not visible when you brake.