Why do the light flicker inside the car and the door ajard light keep popping up?

When you open and close your car door, a contact switch is either opened or closed causing the light to come on or off. The switch is usually located on the door frame some where and it is adjusted so that it has just enough physical contact with the door to operate freely. If you lights and "door ajar light come on erratically while driving, I would think that the switch is lose or out of adjustment.