[Citroënbender]

I'm going to suggest you start with a simple test using something like a 1.2W T-5 wedge globe. Power up the cluster lighting, and "unpick" the wire tails of the T-5, touch one wire leg to each contact pad for a dash illumination globe and see if it lights up.

Silly question, but you have tried both positions (dimmer and brighter) of the dash illumination control?