Originally Posted by diabolik37
I searched the Wunderlich web page (german) but I couldn't find the item N. 8180026. If you can find it and post a pic. I may be able to tell you what it is. In the 2007 GSA you shouldn't need any Gadget to get the ABS to work with a 21" wheel.
Thats the thing, you cant find it, but its mentioned on the page of the conversionkit, thats why i had to mail them instead of ordering the item directly: