One bad thing happened when I got the car back from my mechanic last week... neither headlight will pop up. They both used to be fine. 77 L82 4 spd BTW.

Here's what I know so far:
Mechanically they are ok, I can pop them up and down by hand if I reach under and work the mechanism. They are both nice and smooth.

Vac coming off the manifold is great. I don't know how much but it really .. umm.. sucks.... a lot.
It goes into the filter and the vac on the other side is a bit less but seems ok. It then goes into the check valve and splits off into the dash. Coming out once again it feels less than it was but still feels strong.

Next it goes through a long tube to the front where it connects to the "tank". There it feels weaker. I have checked this hose a million times, it isn't kinked or pinched anywhere. Replacing it may be my next step.

Finally at the other 2 ports on the tank that go to the headlight switches the vac is very weak or dead.

The only thing the mechanic did was zip tie the wires from the ignition system along the lines. I snipped all of them and checked all the hoses for kinks but it hasn't helped.

Any other tricks to try before I just tear it all out and start replacing lines? It was a sudden change. One day it works great, then next, it doesn't.

 

I think you've done a pretty good job of narrowing down already. Keep in mind, it's possible that you have a series of leaks judging by the way you're describing the vac pressure dropping from one line/port to the next. Hoses are cheap providing you're not worried about maintaining a factory look. If you are however, you can get hose kits from Zip or Ecklers for ~$90 IIRC.

BUT before you replace any hoses, make sure your vac tank is holding vacuum pressure. A lot of them have rusted out over the years.

 

I feel that a part of the problem may be the tank as the vac going in is way more than what I feel coming out. Its welded into the frame though right? What can you do if it leaks a bit? Squirt fix-a-flat in it? Bondo the outside where the leak is?

I guess I could blow air into the tank and try to find a leak. Its impossible to do withthe engine running since the fan is blowing there...

The hoses are old so it may be best just to drop $100 on the whole kit with filter and all the hoses and fittings....

 

I don't know of anyone that's actually fixed the stock tank. I think that'd be a lot more trouble than it's worth. The two common solutions are either run the vacuum line directly to the two relays (t-ing it off) or build another vacuum tank from a section of PVC pipe. Obviously the first solution means you'll have no reserve vacuum, but ... do ya need it? *shrugs*

Again, only if you care about maintaining an original look do you need to spend that much on hoses. That money will get you a set of properly color coded hoses in the right lengths from a number of vendors. If you don't care about that, then just head to your local parts store, and get a bunch of plain jane hoses. You could probably replace them all for $30.