why has the illumination for the dials gone on my mercedes 300d?

[JeremyM]

its a w124 1993 k reg 300d

 

[JayP1]

What year is your 300D? If you have a W123 chassis ( '77 - '85 ), they used a fibre optics cable system and one bulb illuminated almost all the dials and switches in the centre console. If the entire centre cluster burned out at once, it's likely the bulb.
If you're referring to the dials in your instrument cluster, as others have mentioned, check the potentiometer ( dimmer ) switch.

 

[JG]

Have you turned the dimmer all the way down by mistake?
If not, could be a fuse.

 

[bingopyjama]

Do you need a new bulb?

 

[fatrab]

Dimmer switch could be faulty, was a common fault on older vauxhalls (sorry mercs were never my thing, havn't worked on many), the potentiometer wore out and the lights would flicker or go out altogether.

Or simply a fuse as suggested above

As suggested below, There's more than one bulb which illuminates the display, probably 4 or 5, so its unlikely they've all gone at the same time, but nevertheless, worth checking!