Mine was the same although the trip out timer was good. I found two solutions:
1. Replace the fuse with a thermostatic one. this will fit in the standard fuse slot (just) and will break the circuit if it gets too hot, saving your fuse box from further melt down.
2. Replace the relay (located just behind the fuse box) with one from a later model. They have an extra pin that will allow you to switch off the heated window at the switch as soon as it is clear rather than having to wait for the timer to switch.
Did both on my '88 GLi and sorted the prob. Hope this helps
