When I turn the headlights on, and the engine is running the doors do not open. Car off, manually open doors, turn car on, doors close, with good pressure. Seems I have plenty of vacuum. I can, with a manual vacuum pump, open either door. I inspected the black w/ green stripe hose, and it appears to be in good shape. With engine running, I pulled the Blk/Grn stripe hose from the bottom of an actuator and there is no vacuum. Might the Headlamp/switch be the issue?
There are a couple more connections before the switch. Original lines get hard and split. Could be anywhere. Since the switch works in one direction, I would consider it good unless I heard a lot of hissing from behind the dash. Check the tank port behind the drivers headlight bulb.
I checked the tank hose behind the driver’s side headlight. Good vacuum to the tank. I also disconnected, removed and inspected the Blk w/ Grn Stripe hose from the firewall to the tee connector at the valance and did not see any obvious signs of holes,cracks.or splits. I took a peek at the switch connector and all hose ends look good.
You need to put your vacuum gauge on the hose and see if you have vacuum.
Today I connected my vacuum gauge to the Blk w/Grn stripe hose at the nipple where it comes out of the firewall. Started the car, turned on headlights, no vacuum registered on gauge. I then hooked remaining Blk w/Grn Stripe hose to direct vacuum and both eyebrows popped wide open.
With a bright light, I looked at the headlight switch under the dash. While working the switch back and forth, I can see the backside of the switch moving back and forth, however the clear plastic piece that the hoses connect to, I see no movement. I’m assuming that when you pull the switch out, something inside the clear housing, moves from the yellow closed position to the green open position. In my case that does not seem to be happening. I’m think the vacuum portion of the switch may be bad. Which means a new switch. 
Installed new headlight switch, and now my headlight doors open and close yay!
Headlight Switch - 1968 Mercury Cougar | O’Reilly Auto Parts
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