Thanks, mystery solved! The wire had broken off the back of the light socket, and that might actually have been the source of the short that burned up my dash main writing harness! Something had burned through the fiber optic cable as well, so the lamp assembly was sitting loose, with nothing attached. I had thought that the fiber optic cable was the wire for the lamp.
pic in this thread shows the tube thingy with bulb in it and the fiber optic strand that takes the light to the tray. [SOLD] - 68 ashtray and slider $25
One year only like many other parts of 68 dash.