intermittent operation of headlights, turn signals and wipers
 

After many years of of enjoying my ML55's, I have recently purchased a 2007 GL450. I love this truck, but the turn signals, headlights, and wipers only work intermittently. I am sure it is some electronic component. However, I am not sure where to start. I tried searching the forums, but found nothing resembling this. The emergency flashers always work, at all locations. Any ideas?