My 1990 500sl had the same problem. It was caused by a switch in the top compartment not being triggered. On my car there is a blue switch on the driver side, about a foot back from the roof pivot. It had a rubber washer the roof pushed on. Over the years this washer had developed a flat spot. I simply spun it to a new position. I figure I'll probably need to spin it again in another ten years. Hell I might even replace it then. Hope this helps.