95 S-10 4.3, 4 wheel drive locked on

My wife accidentally hit the four-wheel drive button on the truck when she was pulling into a parking lot. She said she hit the two-wheel drive button and drove backwards to disengage it but it wouldn’t disengage. I couldn’t get it to unlock even though the 2-Hi button was the only one lit. After numerous tries I finally found a vacuum line that ran to the front transaxle. I disconnected it front the tee in the line and that disengaged the front wheels. What would make this happen? Is there a sensor or a solenoid of something that controls the vacuum to the front wheels? I would like this to work like it used to, of course I could always plug it the vacuum line when I need four-wheel drive, but that just sucks. Plus, am I going to damage anything by leaving that line disconnected? Thanks.