95 4x4 front end wont lock in

The lights on the push button light up when in 4hi or low but front wheels wont lock in.

The lights on the push button light up when in 4hi or low but front wheels wont lock in.
Got good vacuum to it?
What truck and transfer case?
Here is a little info on front Axel actuators.
http://www.automotiveforums.com/vbulletin/showthread.php?t=572914