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...
I know that there is supposed to be a light in the dash ash tray, but mine appears to have fallen off. Can someone post a picture of what it is supposed to look like, and where?