clocks not working?

i have a nissan almera 2000. bought second hand in jan this yr. when im driving the needles on the clovck go to zero showing no milage. its all the clocks..eg..petrol speedometer rev counter etc.. had it iin 3 garages n they cant find a fault,,also got new clocks,,has to be a loose wire somewhere but this doesnt show on a diagnostic tester...