[QUOTE=JWJ;1311839]Last spring when it started getting warm the glowplug light on my '85 MB 300TD stopped lighting up. I assumed it was at least one bad glowplug. I forgot about it until now (when its cold). I assumed I'd have to replace glowplugs but to my surprise the glowplug light is now working again. No trouble starting even in cold weather.[QUOTE]

I agree with the others, the light should come on if only for a couple seconds. I'm fairly certain that if a glow plug is bad the light should flash, not go out completely. This would indicate a lose of power to the glow plug relay, or could simply be a loose or bad bulb (or bad socket ground) in the dash. Being you said it still started fine, I would lean heavily in the bulb direction.