I have a '05 A8L W12. I love the car but have many electrical problems. The latest is the engine fans continue to run and drain the battery. Dealer cannot figure it out and are just replacing expensive control modules. New engine control module said "replace steering column" when powered up. Dealer recommended I donate the car to a charity for tax writ-off! Where can I get an accurate set of wiring diagrams and replacement wire harnesses?