Thanks for the responses to my dash light issue.

Murkybenz: No other electrical issues that I can see. All other dash lights come on as normal and there is no visible flickering of any lights.

Dieselbenz1: The glow plug light doesn't light up at all when it is not working. It doesn't flash and it doesn't come on after the car has started. It acted like that until my recent change-out of all the glow plugs--that was an adventure! Then the bulb worked as normal. Those times it does work now, it lights up when the key is turned on, and stays on until the engine starts, then goes out immediately. The temp sensor sounds intriguing: if the sensor is not working, would that cause the bulb to not light at all?