Funny, I've wondered the same thing. I suspect the stalk mounted switch started on foreign cars and spread to the US. My 62 Austin Healey has a floor button, but my 70 Lotus has the stalk. I beleive Austin Healeys [[and their MG Midget cousins) went to stalk switches in 1969. From a family Chrysler perspective, up to at least the 79 Volare/Aspens still had a floor switch. I know my 74 Darthad a floor switch. Starting in 1978, the Omni/Horizons had stalk switches. After about 1980, at least in the small and midsize Chryslers [[Kcar based), all i remember were stalk switches. Floor switches may have hung around longer on the full size Chrysler cars and trucks.