Cool idea. For the time being (and since I'm not even on the road yet with my '51), I'm going to stick with vacuum wipers. But I'd be interested in the circuit diagram and components. Controls are something I've always been interested in, even though I'm a Mechanical Engineer.
Back in '84 I bought an F250 that didn't come with intermittent wipers. I just bought a different switch and stuck it in and 'voila', had intermittent wipers. Everything was built into the switch. Like you say, nowadays, this is done by black boxes. Opening those up just makes me go "HUH??"