1998 Ford F150 wipers, power windows, 4x4 selector switch,

My 1998 F-150 SC 4x4 was left over the winter in my yard covered with a tarp and the battery connected. When I returned off holidays after 3 months the Windshield wipers and spray, the power windows and the 4x4 selector switch does not work. I had the vehicle into a repair shop for 3 Weeks and first they said it was a faulty gem module which was bought and installed and nothing worked. Then they said it was the fuse panel board attached to the GEM that was not grounding correctly so we go a used one in. They said all the electrical worked that night but the next morning all the above items (windows, washers, 4x4 switch) all failed to work again. they said it could be a grounding problem but Where??? Please give me some clues where to look. this is a great truck other than these new problems....thanks
LNM