There used to be a forum member who made an infinitely variable wiper relay. His name was techguy512, but I don't think he is around anymore. I bought one and love it. I should have bought two...

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palisada plastikowa

A long time ago, I made a circuit for my first car, a 69 Sunbeam Alpine.
It had 2 adjustments. An interval setting and another for the number of wipes per interval. It wasn't my design but one I found in an electronics circuit book.
It was luxury to have that feature back then.