HI,, my rear window didnt work at the switch when i bought my 92, but the key would work it. I discovered that some of the weather stripping had come loose on the bottom of the tailgate. I just reattached it and a couple of days later, both the switch and the key will work the window. Apparently, some moisture was getting into the electricals and causing a short. I have read several threads about rear windows not working due to corrosion causing improper grounding. This seems to be a fairly common cause. I didnt have to get into my tailgate to do anything, but if you get in there, you may find the ground or some of the connections rusted and not making contact.. Hope this helps.
Mike in ARkansas