quadratrac vacuum

My guess is if the switch was bad, it would leak regardless of whether you pinch the lines or not. Well at least the lines that go to the xfer case. If it goes up when you pinch the line that feeds the switch, it could be either the switch or the line. Pinch the line right where it goes into the switch. If the vac. goes up that line should be good so pinch the lines on the output side of the switch. If it goes up, the switch should be good as well. You should probably cycle the switch and repeat the previous step. Now go down to the transfer case and pinch lines there, one at a time. One of these lines should be the culprit at this point. Again, I think you will need to cycle the switch to be sure of which one is the problem. In any case, the system is pretty simple.

Tom Greening did pass the time by typing:

I use one of these for testing vac lines. But be careful. Never go above what the device your testing can take. In most cases 12" of vac. The gauge will then tell you if there is a slow leak. And with an assortment of golf T's and plastic caps you can work your way down the lines to find the leak. For hardline/softline mixes it's usually where they fit over each other. That can be fixed by a bit of glue or thin sealant.