Light source for fibre-optic illuminated switches - '81 300 SD

Does anyone know where the light bulb is for the fibre-optic leads that illuminate the rocker swithches on the upper centre console? I have taken out the instrument panel (doesn't seem to be there,
although I did fix the loose bulb that was intermittent on the left side of the dash) and I have removed the wooden panel that holds these "dark switches". I can see that the fibre-optic cables go off somewhere under the dash, but I would like to have a better idea of how much more I need to remove to find this mystery light source.
And why didn't Mercedes just use LED's like they did on the window swithches on the lower console?
thanks for any suggestions
Gary
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The bulb that lights the optics is to the left of the AAC pushbutton assembly. You have to remove the ashtray assembly to get the ac wood off.

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