https://www.hagerty.com/articles-videos/articles/2018/01/31/the-year-cadillac-gave-drivers-the-electric-chair?utm_source=SFMC&utm_medium=email&
An interesting article for your consideration. Happy Day, James
Cadillac was ahead of the game on this one. Interesting how it worked though -- "It only operated with the engine actually RUNNING by means of detecting generator-output to control a relay; secondly, this relay was shut off once a water temperature sensor indicated the car's coolant was warm enough for the heater to provide "adequate heat". (The 75 Series Limousines had this option only available for the rear seats). I guess that prevents you from being grilled like a toaster. ;D I recall hearing stories that this system was erratic and potentially dangerous, and thus Cadillac pulled it. Maybe somebody who knows mid 1960's Fleetwoods would know more? Fun read.....
I thought it was still offered in 1969? However, in any model year it was offered, it was "rare" to find a Cadillac equipped with the heated seats.