It's the internal coil circuit inside the distributor. When it heats up it ends up causing a short. Simple fix is the HEI conversion and external coil.
http://www.clubprotege.com/wil/howto/hei/index.htm this is the walkthrough on the conversion , I think it costs about 60-ish and maybe 2 hours for a novice. When I had my 1993 I had the same thing happen to me repeatedly and at a cost of 300 + for new distributors..it was a expensive problem.
Also mx-3.com may end up being a little more resourceful for you.