93 GMC Jimmy, four wheel drive stopped working

The four wheel drive in my truck will no longer come on. It has an electronic switch to turn on 4-High or 4-low, and neither one will come on. If its in park and I hit the switch, nothing happens. If its in neutral, the light on the switch flashes, I can hear what I think is a relay clicking on to the right of the dash, then the light goes out and nothing else happens. My mechanic said (from what I told him over the phone) that the flashing may be an era message, but wasn’t sure. Any help is greatly appreciated. I park in my back yard, and got stuck last week. Had to have AAA winch me out. That was embarrassing. lol.

I doubt if this your problem but I had a '99 that the wires to the shifting motor got burned by the exhaust. You might check this.