Sometimes, (2/5 times), when I turn on the ignition, there is no power to any of the windows or the sunroof, and the switches do not illuminate. If I open the driver's door, the power is restored to the windows & sunroof as the interior light comes on. Closing the door cuts all the power again. The power is restored usually within about 15 mins of driving. I'm guessing perhaps a relay is sticking? Can anyone suggest what & where to check?