The TSBs are worth a read and may help. See:

http://www.hamtramck-historical.com/library.shtml

and scroll to bottom. Read "Understanding and Using..." first.

The Plymouth TSB for 1970 in Chapter 8 Electrical has testing procedures for wipers, as does, of course, the FSM. There are other wiper TSBs for other years, including 69.

If you don't see two dolphins, you need a vacation.