4 wheel drive does not work. tranfer case engages.

 

There are switches and relays in the system that could be bad. but the most common cause is the solenoid on the front axle that engages the front diff. Remove the solenoid and with jumper leads from the batt hook up to solenoid terminals and watch it. It should move one way, than reverese the leads and it should move the other way.It is a little slow, so leave the leads hooked up for 30 seconds or so.