Speedo/Rev Counter Illumination
 

For a while now I have had the rev/speed dials weirdly dimming and lightening without accounting for the ambient lighting conditions. They have now failed altogether. The indicator needles are ok.
Any clues as to where the fault may lie and where to start? Ambient light sensor? Some controller in the dash?

Could be the sensor, but what happens when you turn the headlights on/off?
And when you play with the brightness buttons?

Nowt. Although when I tried the brightness buttons the other day they seemed to result in spasmodic and intermittent results.

So probably not the actual sensor then.