When I push the 4 wheel drive buttion . The light

Check to see if the front diff is being engaged. Ther is a vac switch that come from the transfer case. It sits right on top has 3 lines. One line is vac input the other is vac output the third is a vent. When you push the 4wd button that switch allows the vac to the front diff. The front diff actuator is under the battery. Check to see if the actuator is moving if not check to see if the switch is any good by checking vac on the actutor line. You can doo this with out taking out the battery. You will see a line that goes from the back of the engine up the right side then under the batt. It is covered by wire loom. Cut in to it and see if there is vac. If not check to see the switch works. If there is then check to see if the actuator is torn( actuator looks like a cruse control actuator) or the cable to the front diff is stuck.