Amazing what you can learn by reading the factory service manual. I just browse through it sometimes and learn how a part of the truck works.

The thing to keep in mind is that it isn't this huge complex monstrosity that you could never fully understand. Like everything else, it is a bunch of simple systems put together.

I find that helps me... you don't need to know how the whole truck works today... if there is a problem with the brakes - just learn how the brakes work. No single system is really that hard to understand.

Howstuffworks.com is cool, too.