recently my windshield wipers have quit delaying like they should when you turn the switch over one click....they work,but they just go steady, like theyre on the 2nd click....pardon the technical terms....what could be the culprit? is there a relay that controls this in the fusebox?

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1985 300SD 192,000miles...Astral silver/ Grey MbTex

1983 300D 194,000miles...White/Tan MbTex...my newest addiction