vacuum

I have done a fair amount of research on this, but I am stuck. I have a 1999 jimmy with the 4 switch 4WD buttons including auto. I cannot put it into 4WD. Here is what I know: 1. I have the 4WD with the two wire actuator on the firewall that controls the vacuum. I have included a picture...

We have a 1994 GMC Sierra 2500, 4WD HD with automatic, A/C and a 350 V8. It has a round vacuum reservoir with two hoses and it's not connected. The Internet using Google has yielded ZERO useable info. I find the round vacuum reservoir - but they show only one hose coming from it. Heck, all we...