Relay is black-box - no way to test it far as I know.

They're quite a few bucks from the dealer, but do show up from time-to-time on e-bay.

If there are problems with the combination relay, I would think that the problems would affect other systems besides the wipers - but maybe not.

I my case, the wiper relay was the issue. Sits on top of the fuse box lid - less than 5 minutes to R&R.

Board member Eddie A is parting a pair of 140s - I'll bet he has one or more wiper relays for sale. Good fellow to deal with - prompt shipper and reasonable prices.