Audi A4 - lights on Heater Blowers

Does any one have any ideas why the lights for the heater blowers on my A4 2.0 Sport 2001 (newer shape) do not light up??
I have played with the '+ / -' hoping these would light them up, but this has not worked (however everything else on the dash goes duller or brighter)..
It seems strange why the lights just for the heater blowers switch (Drivers side, Passenger, and bother centre console) dont light up. Every single other bulb / LED works fine.
Does any one know if all these lights could use the same power source or controlled from a certain fuse maybe?
Many Thanks
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