That's not something I've seen, except when accompanied by the windows going up and down and the mirrors folding in and out of their own accord (which is solved by disconnecting the battery).
If you do have the sensor, it is a big circular patch in the centre of the windscreen at the bottom - but the automatic stuff shouldn't work unless you have manually wiped the windscreen once (to stop the car trying to wipe when there is ice on the windscreen, I assume).
That just about sums up the 807 electricals. Mine has just spent a month(!) at the local dealer after a couple of dozen previous trips with electrical issues. It came back, supposedly all fixed, and less than a week later had electrical problems again.
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