2000 A4 Climate control only with lights on??

I have a 2000 A4 TDI which has developed a fault with the climate control. If the headlights or side lights are on the climate control works perfectly.
If the lights are off it exibits trange behaviour. The temperature "-" light is on all the time, the temperature "-" button does not work, the fan "+" & "-" buttons don't work and the recirculation button does not work. Repeated pressing of the temp "-" button sometimes lowers the temperature and sometimes switches the air from "auto" to face vents!
Anyone seen anything like this?
Thanks,
Jim.
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