I was sent a a Buchla Music Easel for calibration and repair that consisted of an early version 208 and this 221 Kinesthetic Input Port. This module is quite interesting in that the entire module will "wiggle" side to side as a modulation source. This module was fully functional so I did not remove it from the cabinet.
The side-to-side wiggle function is implemented through two light dependent resistors mounted on the PCB. They modulate the bend CV which is added to the keyboard CV. The three blue banana jacks in the Key Activated Voltage Sources area are the keyboard CV, keyboard CV+bend CV, and keyboard CV+bend CV+portamento.
The illumination source for the two light dependent resistors is an incandescent bulb fastened to the bottom of the boat. It is soldered in place with a shield over the top.