It's the knob on the cable to open/shut the "door" on the front of your deluxe heater. On earlier years the knob/cable open/shut the defrost diverter (in 54/55 the defrost diverter is a knob/lever right on the heater and it is moved by hand).

Tim

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.