Andrachuck [bless his heart] nailed it! Every Series III eventually won’t park its windshield wipers. Two things to try: The EASY one: On my '87 III Vanden Plas, to park my wipers I have to push the wiper wand DOWN after shutting them off. If that doesn’t work [and it caused a forehead smack to me!], replace the wiper park module [at this writing 11/2019, $50 from JagBits]. Remove the battery and on the fender you will find the wiper motor with the plug-in park module at the front. Pry it loose, replace it, and Bob’s your uncle! Yes, you can rebuild the module. No, for fifty bucks it isn’t worth it.