I had the rear defrost quit working on my '89 Conquest TSi.
The fuse was fine. The wiring and contacts at the window were good. I found one spot in one of the lines on the window that appeared faded. I bought a repair kit, which was some type of a liquid, similar in style to Whiteout, and applied it to the spot. This fixed the problem.
All that being said, check the contacts on both sides of the window, check all of the lines, and make sure the switch is working.