There is a decal set that you can get from the vendors that looks like it belongs just below the defroster control arm. Maybe its not for the Harrison Deluxe heater?

http://www.classicparts.com/1947-54-Defroster-Instruction-Decal/productinfo/68-555/#.VnM_qBUrKHs


Deve

1950 Chevy 3100 Deluxe Cab
1950 Chevy 3100 Standard Cab
In the Stovebolt Gallery
The Think Tank
More info and tips at Deve's Technet