Mass error - Workshop in Greater Bonn

Hello, everybody.
Unfortunately, my V8 has a ground error in which the entire rear lights fail when the engine is running. The switch for high-light and turn signal has just been changed.
Someone knows a workshop in the Greater Bonn area, which is familiar with the electrics of the V8. Unfortunately, most of them no longer have any documents for the Audi.
Thank you and greetings

Alfred