Note: The electronics of the rain sensor reacts to the electrical conductivity of the water. We have now ascertained that there are areas where rainwater falls, which is absolutely clean (distilled water). The sensor does not react to this. The water must be at least slightly contaminated (fractions of dust, smoke, etc.) so that the water is electroconductive and triggers the sensor. In Germany the rainwater is conductive in 99% of the areas. If the sensor does not trigger in your case, you should install it in such a manner that the rainwater runs at first over a small porch roof or the like before the water touches the sensor. If the water falls directly from the cloud on the sensor in its purest form and does not trigger it, it will be sufficient if it runs over a small board or from a porch roof on the sensor. Then the water will have absorbed enough impurifications that it will be electroconductive and triggers the sensor. Of course, the sensor has to be built it slantwise so that the water runs down again.