Classic/Antique Car Repair: 1976 Lincoln headlight doors, vacuum hoses, headlight doors

Question
Hi, i have a '76 Lincoln Town Coupe with vacuum operated headlight doors.  When i first got the car the headlight doors would stay shut after shutting off the engine, then open after a few days.  Now the doors close after starting, and open immediately after shutting off the car.  A mechanic told me that there is a black round disk about the size of a half-dollar by the coolant overflow, and that inside this disk is a valve that shuts to keep the doors shut when the car is off.  I found one in a junkyard and installed it but no luck.  The disk has 2 male ends on each side and connects the vacuum hoses on each side.  I was wondering your opinion on this before i go back to the junkyard looking for another disk or start replacing the miles of vacuum hose.

Thanks

Bob

Answer
That gadget, the black round disk is a one way check valve and can be tested easily. It allows vacuum to flow in one direction only. Now if you are going to diagnose this system I would advise the purchase of a MytyVac tool. It is a hand held vacuum pump. The check valve should allow vacuum to flow through in one direction and hold vacuum in the other direction. The tool will be a great aid in diagnosing the system.