Potentiometer - Whazzit?

[PropFan]

This little knob is hanging down from the panel on the pilot's side. I ran it through its full range of motion with the master switch on, and I could not discern any effect on lights, radios, etc. Most importantly, the wings did not fall off.

Any idea what this controls (or used to control)?

 

[JimC]

 

[N4655R]

 

[flyguydon]

 

[Domenick]

 

[Tweety]