mercdes vito 112 speedo/clocks, lights stay off until warm?

mercdes vito 112 speedo/clocks, lights stay off until warm. seems to be worse when foogy or damp out, theres nothing for about 5 mins then they come to life start flickering and then work perfect once its warm inside. well strange. any help please as i feer they may stay of soon as it seems to getting longer before they work
thanks