1996 Jimmy, tailgate glass wont release

I have a 1996 GMC Jimmy, the rear window and tailgate will not open, when you try to open it with the key or tailgate button I get a buzzing sound but the glass will not release, the same thing happens when you push the dash button. It will not open with the inside handle either. I can not get the panel off because the tailgate is closed and the panel screws are on the sides of the tailgate. How do I bypass the electric switch in order to release the glass and to drop the tailgate?

If neither the switch nor the key open it, then there is only one alternative. That is to open it manually. And for that you have to take the cover off, which will come off while the gate is up, just not easy.