Look back through the early to late 70's & 80's madel year cars from Detriot. As I recal my parents bought a Ford station wagon that had a moisture activted wiper system as a standard option. But cannot remember what year model it was.

Many current models of Peugeot cars on sale in UK are fitted with an auto wiper system.  The sensor is fitted on the inside of the windshield and I believe uses some sort of infra red beam reflection/scatter detection of raindrops on the outer surface.  I drove a loan car fitted with such a system,  without being aware of it,  and was taken by surprise when the wipers started up as I overtook a lorry throwing spray up of the road and was amazed that the speed of the wipers also varied depending on the intensity of the rain/spray.