The intermittent function for the wiper does not work in my 1994 e420. Well it’s more like it doesn’t work 98% of the time; every once in a great while it will work. If I just leave the switch on the setting it will randomly activate a while later, but not always.

What is this I hear about a wiper relay and or wiper control module? Where are they? Is one of them the more likely cause? Can I fix them?