yes the heaters were ALL optional - there were 3 heater versions: the bottom of the line one was only dealer installed,, the middle one was a factory installed 'standard' ["recirculating"] version that had no cables, just a 3 position fan switch, and a factory installed deluxe model w/ the fancy control unit [tho they could also be dealer add-ons]

that option stuff is how GM and the dealers made the gravy grin
see the manual here , HEATER & DEFROSTER (DELUXE) - Truck RPO #987641

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics