I have a '05F-150STX 4x4, my 4x4 isn't working, light comes on in dash when engaged, but no 4x4, should i have vacuum at hubs when engaged in 4x4 or not?

 

My understanding is that no there should be no vacuum when in 4x4. The default position for the IWE's (hubs) is locked. Engine off they are locked up and do not unlock until vacuum is applied when the engine is started. More than likely, your problem is something with the transfer case. If you have electronic shift on the fly, it is probably a problem with the TC shift motor.

 

he is exactly right, no vaccuum unless in 4x2 with engine on

 

I have vacuum in 4x2 and vacuum in 4x4, so i'm thinking possibly vacuum solenoid on firewall behind battery is bad, right?

 

Good possibility. Either that or what controls the solenoid is bad. Not sure whether that is the GEM module or something else.