I'm trying to troubleshoot an issue with the defroster switch in my 83 300TD.

The rear defroster operates, and the light indicating that the defroster is on illuminates, but the switch does not do the courtesy glow like the other upper dash switches (when the headlights are switched on, it does not illuminate like the other switches).

I removed the switches to have a look and it only has one fiber-optic connection, whereas all the other switches have two connections. I see light coming through the fiber.

Does anyone have any ideas? Could the switch simply be bad?