Well I've done a lot of reading on this vac switch and 4wd.
Anyways: what got me started was the random vibration / whinning when driving in 2wd; sound like I was driving on rumble strips.
If I put it in 4wd the sound would immediately go away, and I could usually go back to 2wd also then.
So tonight I changed the vacum switch on the T.case and changed the t.case fluid; while I was down there... find out that it was over full... figures; input seal.
Also changed front diff fluid.
On the Old vac switch: the ball seemed to be stuck IN, the new one the ball was out further and moves in and out.
I start it up and now have NO 4wd. Light on 4wd button is lit up.
So I put the old vac switch in for now, and my 4wd is back.

Obviously I need to get the input seal changed, but my question is... why didn't the 4wd work with the NEW vac switch ??? The vacum hoses only fit on one way with the "little key" that is between the two hoses.