sunroof and horn work intermittently..fix?
 

I own a 1999 E430. sometimes I am able to open its sunroof normally. when I am able to do this i am able to honk the horn. other times i try to open to the sunroof and i does not open, when this happens the horn doesn't work either. this seems to happen randomly. how do i fix this? It seems the horn and the sunroof are on the same electrical circuit