The patent came in 1969. By that time we had put men on the moon but intermittent wipers were a mystery to mankind? How are they more difficult than traffic lights, for example? What was the stumbling block?.
(Yes, I ask this because of the movie. No, I haven’t seen the movie. Yes, it is ok to reference and spoil it, if necessary)
You need an electronic timer and relays that will hold up to a 5 amp draw. Just a guess.
Nothing.
But someone had to be first.
Timing is off. Here’s a neat timeline.
This Wikipedia article also pretty objectively covers the issue, and specifically address the OP’s concern as it relates to “novelty.”
The wiki entry doesn’t seem to explain what is it that makes them unique or novel or what was the technological hurdle.
From the timeline, it seems that there had been plenty of similar inventions before, which is basically the point of my question. Things that went on and off existed before intermittent wipers. What was so special about wipers that car companies couldn’t get to work?
An intermittant wiper is more than something that goes on and off – it’s something that goes on for exactly one sweep of the blades, then turns off, then repeats. The novelty is getting this to actually work.
Ed
My guess is that by the end of the 60’s semicondctors were becoming cheap and common. (Most complex electronics items, like televisions still largely relied on tube technology at the time, but it was on the way out.
Trying to build a reliable circuit that could control windshield wipers using tubes, capacitors and relays was possible, but would have added considerable cost and how ever well designed would never have had the reliability of the same basic idea in solid state (semiconductor) electronics.
Just my 2 cents
regards
FML
Why not just a mechanical device? You just need a regular wiper motor, geared up, with a device to make the linkage between the motor and the wiper slip for 2/3 of the cycle. Not saying I could perfect one in an evening, but certainly seems to be within the resources of a small team of engineers at Ford.
Actually, the timeline Balthisar linked to shows that the manufacturers were playing around with using a bimetal strip as the timing device. This would might be more accurate than a timer made of tubes, resistors and/or capacitors, and it would certainly be cheaper and more reliable.
What did high-end cars use before? Wipers with mechanically or electrically adjustable speed? Or just on/off?
The man with the red flag also carried a cloth. 
Oh, I meant that article as a means of addressing the OP in the sense that they weren’t at all novel.
Before intermittent wipers, cars usually had 2 wiper speeds, slow and fast, similar to the non-intermittent settings on today’s cars.
And before that, cars had vacuum wipers, which tended to stop when the vacuum went away (going uphill, passing). Wheeeee!
This I can see, but then it is just a matter of acquisition of technology, not a flash of genius. Just as nobody had invented maglev trains before superconductors, not for lack of the idea but of the means to carry it out.
The genius is in figuring out a way to do it that is simple, cheap, and reliable.