What is the cause and the solution of a 1992 Ford Explorer with push button 4wheel drive being stuck in 4high?

I have a 96 Explorer - had the same problem. There is a side cover on the transfer case, behind which is a small electric motor and a gear drive that switches the transfer case from high to low. I cleaned up this worm gear and re-greased it. Works fine now. I presume the problem was that since I hadn't used 4low for a long time, the grease on the worm dried out and caused the electric motor to thermo out and not run. Works now. Read this faq to do it yourself for free: http://www.explorerforum.com/Singleton/web/pages/tcase.html