This may sound like a, "Is the power on," question but...
Are you sure you don't have the feature? This one is pretty standard. I'd be surprised if you didn't have it. Of course, I'm sure there are exceptions, but I'd be really surprised.
Wiper switch needs to be up one notch from the off position. Then the rheostat on the face of the wiper lever/switch adjusts the sensitivity (down=less, up=more).
I suggest a thorough check here first, because one of the components needed is a thin film between the windshield and the rain sensor. I don't think the film is sold as a separate part from the windshield (though I vaguely recall someone here may have sourced it?). So, at the very least, the windshield needs to come out to add the film between the rain sensor (after you retro-fit it) and the windshield. At worst (on top of all the components that would be required), the windshield would need to be replaced.
My recent experience was that no aftermarket windshield source included the film, and the installers (2 different companies) were unaware of it (after windshield was replaced twice). Windshield had to be ordered from dealer, then their preferred vendor installed it. Now all is well. Lesson learned.
2005 A8L 4.2 Silver on Black Leather / 5K range HID Headlamps / Fog Lamp Conversion to 3K range HIDs / Interior LED Conversion / Multiple VAG changes to suit (more coming, as nuggets are uncovered) / 19X8.5 Turbines with Conti DWS rubber / AMI Upgrade / Parktronic upgrade
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