There are sites and products that we are happy to support - we only list those that we have direct experience with.
Rob Siegel has written a book to help the enthusiast walk their way through their car's electrical systems - something near and dear to our hearts! Don't be afraid of this book - it's written (almost) like a novel, and it's written at a level that pretty much anyone can relate to. It contains so many wiring 'basics' that I think it's a benefit to owners of all vehicles, but it's a must for BMW, Audi, Mercedes, MINI, Porsche, and VW owners.
If you need electrical parts for your BMW, Ducati, or Moto Guzzi bike, I can't recommend these guys enough.