4wd problems

Ok so I have been trying to fix my 4wd this summer. I have tried to fix a few things with no luck I have a 2000 jimmy I have replaced the following:
1st the switch on the front axle Switch
2ndI was still not getting anywhere and it would work when it wanted to. I could bypass this vacuum switch on the fire wall and the 4wd works great but I want to fix it right. So I went to the dealer and bought a new one. Put it on and still no luck.
So still not having any luck so I thought that maybe the switch was just warn out. I could hear the transfer case switch in and out but thought that maybe it was not getting a single to open and close.
I want to make sure that I have the vacuum line on right can someone look and tell me what the bottom one goes to and what the top goes too. I can feel the air come out of the little breather hole on the top of this little black thing but not sure why it is open when it should be closed?
3rd So was at the local parts store picking up some oil today and see this 4wd switch sitting there on a hook and bought it. I installed it and same thing. Still nothing, would love to figure this out before the snow falls any help would be appreciated.