There is a manual switch with the following printed on the switch: "EXT" on top of switch "INT" on bottom of switch. There is an illegible ink stamp on the wiring side.
Date
1979 ca.
Manufacturer
Xerox PARC (Palo Alto Research Center)
Identifying Numbers
Other number
11 79
Silk screened on component side of board.
Other number
216341C
Labeled as "PWB NO." This number is silk screened on component side
Part number
216339E
Labeled as "ASSY NO." The numbers are silk screened and the "E" is ink stamped