Problem with Cab dome light

The dome light in my truck only works about half the time. It's controlled by a three position switch on the dash. The three positions are cab dome, door, off. When the switch is in the door position the light is supposed to turn on when the door is open. The courtesy light on the bottom of the door is also supposed to turn on. These lights very rarely turn on when I open the door. But they will on rare occasion. The light is supposed to turn on whenever the switch is in the on position. This function works about 50% of the time. I am wondering if anyone has ran into this problem before and what the fix was. I'm pretty sure the body controller has no control over this function. So the problem should be in the switch itself on the dash. For example, I just turned the light on by flipping the switch to the cab dome position. I then immediately flipped it back to the off position and the light went out. I then immediately flipped the switch back to the cab dome position but the light does not come back on again. Please chime in if this sounds familiar to you. I have an 09 Prostar by the way.