This has probably been gone over before but I'm new here so here we go anyway.
I bought a 96 Jimmy this summer that had been sitting for sometime...the guy said the 4X4 worked good but when I put in 4-low the rear differential locks in but not the front...I get nothing a 4-high...the buttons light up like the should...I looked at the Vacuum Actuator but I know nothing about it...This is my first 4X4...any help would be appriciated...Thanks

 

most common problem broken or cracked vacuum line it's very cheap and easy fix, checking the condition of the vac lines would be my first stop (while your in there inspect the actuator make sure there are no rips in the diaphragm on the actuator) if it sat for awhile as the previous owner told you dry rotted and cracked vac lines are quite likely.

 

Thanks...I did fix one vacuum hose that hooks up to something on the intake next to the throttle body...I have no idea what is for.