I have a 2009 3.0 TDI SE. Despite having it 3.5 years I haven't figured out how to dip the rear view mirror. There appears to be a on/off button on it and a light glows red or green after pressing it. However, neither on nor off seems to make any differene to the dazzle I get from vehicles behind me when driving in the dark. It's probably something obvious but not to me alas - any suggestions?