My 86 has a wiper problem also, I believe you have the same setup as I do,
do you have the slider with the pull down to mist? well, these older cars have
issues with oxidation in the connections, the "logic" from the slider plugs into
two accessible connectors on the wiper motor and one not so accesible, pulling them off and cleaning them with contact cleaner, the switch in the
door is hard to get at, but spray the cleaner down into the switch and move
it back and forth a few times, give it another spray and exercise it again.
If that doesnt work the shop manual has a pretty good test routine to trouble shoot the citcuit, you need a Digital multi-meter, you should have a meter if you own one of these cars!