How do I tell if the master vacuum switch is bad in my 80' 300D?(the black thing in the main door with 3 outlets) I disconnected the three lines going in it and I dont seem to feel any suction when i put my fingers on them. None of my locks are working by the way. How do I also find out if the yellow check valve is bad? Its doesnt leak I've already ckecked it for that. And another thing the 2 yellow lines going through the fire wall where do they go? I think 1 goes to the main door and the other I'm not sure, the vac tank to the trunk?