Hey Hollywood. Look at your front axle. If it's a dana 60. It'll have a vacuum controlled servo on the axle to disconnect the axle when it's shifted into 2-wheel drive. Check for vacuum at the servo with the engine running and engaged in 4-wheel drive. it should have vacuum. if not follow the line to the switch on the transfer case. the vacuum comes from the engine, to the switch on the t-case. The switch turns the vacuum on and off with gear selection. If the servo has vacuum and it switches fine with t-case gear selection, try tapping on the housing lightly with a hammer. It may just be stuck. the light is switched on and off by a switch on the servo itself. If you have vacuum at the switch on the t-case, but it's not switching it to the front axle, the switch is bad. If you have good vacuum control but it still wont shift try pumping up the disconnect servo. it may have a ruptured diaphragm. If the light is'nt coming on, it's telling me it's in the servo, the vacuum switch, or vacuum related. here's a picture of the disconnect servo. I hope this helps..