I know the Facts sextion says this, but just making sure this is the case for the 04 cavs as well.
Brown - Left Rear Speaker Output (+)
Yellow - Left Rear Speaker Output (-)
Dark Blue - Right Rear Speaker Output (+)
Light Blue - Right Rear Speaker Output (-)
Just becasue isn't the darker wire usually the negative terminal on most things.
On the rears it's reverse, darker is positive usually.
-Chris