1999 chevy tracker,4wd problem

Can anyone send me a diagram of the four wheel drive system on a 99 tracker?I see the unit under front bumper,is it pump or vacuum operated?Hubs seem fine,axels & drve shaft aLL GOOD,but no 4wd.Please help.

I also have 99 tracker with similar problem? no 4wd -no 4wd lite. the airpump should have 5-10 lbs air. my pump has 6 llbs, works for 10 secs, then quits. front axles wont engage.