I have been a professional mechanic for a little over 20 years now. In those 20 years, I have worked on big over-the-road trucks, farm tractors, little import automobiles, ambulances, school buses, and now FedEx trucks and ground support equipment. In between, I've worked on lawnmowers, snowblowers, garden tillers, and the odd occasional motorcycle.
I've never claimed to know it all, or to be an expert at anything. But I do know that the biggest part of being a good mechanic is knowing where to find the information you need to diagnose and repair a vehicle, whether it's a VW or a KW.
Here are some sites I have found on the Web that have something to do with the way I make my living. Check 'em out!
Automotive Service Excellence
Cummins Engine Company
Omaha Truck Center
Snap-on Automotive Diagnostic Tools and Service Equipment