1999 chevy blazer 4x4 doesnt work

[ndgrown]

hi i am a new member
i have a 99 blazer that the 2wd light is on but when i press the 4hi button all it did was flash for about 5 min. and then go back to 2hi. i have replaced the transfercase motor with one from a junk yard but no change. fount out that there was no vacuum comming out of the switch on the firewall to engage the front axle. if i put vacuum on the actuator manually and then put the 4hi button it engaged. before i was able to replace the switch the service 4wd light on the dash came on and the lights on the push button went out. anybody have any ideas?????