Here is what I know, you can draw whatever conclusions you wish.
Heaters for AD trucks are accessories not factory options, they carry a part number not an RPO (see the 1947-48 exception to this rule in my later post). There are three distinct heater types, the early version in some 47-48's that was a carryover from the 1941-46 years. This heater when equipped with the defroster (Deluxe) comes with two Delco or Cole-Hersee switches.
https://www.flickr.com/photos/advance-design_parts_co/15859483512/in/set-72157631868452754https://www.flickr.com/photos/advance-design_parts_co/15860119645/in/set-72157631868452754The recirculating unit comes with the one switch, all of these I have seen have been Delco.
https://www.flickr.com/photos/advance-design_parts_co/8129444438/in/set-72157631868452754The Air-Flow style unit again comes with a switch as part of the kit I have seen Cole-Hersee and Delco.
https://www.flickr.com/photos/advance-design_parts_co/8129413707/in/set-72157631868452754The unit comes with all the parts to install because nothing is installed on the line, block-off plates cover the holes, the rest is not included. This is a flat rate job with price guides quoting both the installed and list (unit) price.
https://www.flickr.com/photos/advance-design_parts_co/8131119579/in/set-72157631872034068For dealer (or owner) installed heaters other than the three mentioned above there were numerous manufacturers, Alvin, Montgomery-Ward, Firestone, Sears, B.F. Goodrich, etc. you could have any number of switch and installation parts included of course.
https://www.flickr.com/photos/advance-design_parts_co/8377831744/in/set-72157631868452754Now if a dealer bought his own GM manufactured units (complete kits) which makes sense since they are a dealer (expected to purchase a yearly defined quota). Those units were assembled and distributed by the General Motors Parts Division (many NOS parts are marked this way) those units in my experience contain Delco or Cole-Hersee switches, not Ark-Les.
For comparative purposes in the period of time I am talking about, GM was the second largest employer in the world (Soviet State Industries was first). In 1955 GM became the first company to pay over $1billion in yearly taxes. They had the necessary divisional products (or partner products) to fill these kits and their dealer's parts shelves.
