Manic intermittent wipers!

[CANEX]

Does anyone else have manic intermittent wipers?
They seem to have a mind of their own - dont work when it's raining - then go double speed when it stops
None of the settings seem to make any difference & I've tried cleaning the glass

 

[CANEX]

is there supposed to be some kind of tape on the windscreen sensor?
here are a couple of pictures of my sensor but I can't see where any tape would go?

there are a couple of scratches on the sensor surface - I wonder of they would make it intermittent?