Back when men were real men, you didn't have a heater. No factory installed heater. A heater was optional.

The link to a previous discussion:
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1140805/1946_Chevrolet_Truck_heater.html

A fused heater switch mounts to the bottom of the dash.
The heater takes a lot of current so I suspect it was not connected to the ignition switch.
Most likely the ammeter.
Forgetting and leaving the heater on would run down the battery.
I would add a relay that is operated by the ignition switch.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."