About the wipers.....

Go to your fuse box, which is under the hood on the left hand said of the firewall, and pull the fuses one at a time and clean the ends of the fuses and the inside of the clips they go into. I have found this is almost a standard thing when picking up an old Porsche, Mercedes or Volvo that uses the types of fuses that were then in use.

This may not fix your problem but it is something that usually needs to be done. And if nothing else will eliminate that as the source of your trouble.

Also check for a straight up burned out fuse. Some of these fuses have very thin filaments and they build up electrical resistance over the year. Replacing them all with new ones is not an expensive thing.