4WD system

I have as many others have found, a non functioning 4WD system and am planning to add manual free wheeling hubs.  I understand that I need to block off the vacuum lines but nowhere have I been able to find information regarding the drive to the front drive shafts.  My question is simply - how do they work and what engages them?  Do they need a functioning vacuum system or are they turning freely until the vacuum of free wheeling hubs are engaged.

I am sure someone will be able to answer my niave question.
Stalker

Drive to the front axle is engaged inside the transfer case when you select 4wd. It is not part of the vacuum system, but on push button 4wd models you need to trick the system into thinking the vacuum system is still working.

Many thanks, I assume that the switch activates an electric motor somewhere to engage the front axel. Is there any way to check that part of the system is functioning properly?

Kind regards

Yes there is an actuator on the transfer case that engages drive to the front axle when you request 4wd. The system is self diagnosing. If it's working you get a solid 4wd light once engaged. If it's not working you get flashes and beeps.

many thanks again Busta,