Glenn,

It is actually the control cable for this directional signal I found on a 1954 farm truck. You pull the lever and the arm goes up to signal. The guy I bought the truck from says it was pretty popular here in the west for signaling the combines as they were filling?
https://www.flickr.com/photos/advance-design_parts_co/8129047985/in/album-72157631867396207/
https://www.flickr.com/photos/advance-design_parts_co/8129080864/in/album-72157631867396207/
Here is the arm as installed on the bed of the '54.
https://www.flickr.com/photos/advance-design_parts_co/8130556264/in/album-72157631870734114/