I just pulled my relay off, unknowing whether it was the culprit for the same problems you guys are having, essentially, cookey behavior from the wipers at seemingly random times.
My wipers stopped about 2 years ago at 70mph on the freeway in heavy rain. After removing the solenoid and hearing a $40 dollar price, I reinstalled the relay to do some diagnostic work, and the wipers worked again (thought it might have been a contact issue). Even though I don't think the auto sensor mode has been working for the last couple of years, I have typically had the wipers working and it didn't seem worthwhile to replace the relay, until a 50 year blizzard hit south Texas and stranded my pregnant wife. Had I known how easy the relay was to service, I would have fixed the problem a long time ago. I was going to detail the process with pictures and such, but I happened to find this link (www.dgce.co.uk
) tonight as I was preparing to write down the process. He does a pretty good job of documenting the repair, and even though I did it a little different, if I have more problems, I will probably resolder the contact like he does to make it a little more reliable. I will let you know in 10 years when I have to service it again (fingers crossed). Let me know if you have any questions. This process takes about an hour start to finish, and I could do it again in about 15 minutes if I didn't have to play around with the terminals to determine what went where. I listed a few pictures for some reference as to what were talking about.
Relays are primarily a mechanical switch, that is driven by an electric solenoid. This enables a low power circuit to drive something needing much greater power. You can test the two solenoids by applying a 12v differential between 5 and 8, and 5 and 9, where 5 is at +12v. If you don't get clean action, the relay is certainly your problem. Open the relay up (pry the hooks/tabs out with 2 screwdrivers and pull the black piece upward) and look for the two contacts, where the thick spring-loaded copper wire terminates in between two plates. One or both of your contacts is likely a little dark. The problem in my relay was that the driven wire in the relay had frayed at the contact, causing it to arc against the terminal when it was in use. This caused carbon buildup on the contact, making it stick. I cleaned out the contact area with a thin piece of 180 grit sandpaper, and removed the portion of frayed wire from the line that caused the arc.