One of the problems with wiring diagrams from any source is being able to interpret how the circuit functions.
With more control units, or for the want of a better expression 'black boxes', diagnosing the problem even with the correct diagram, can be a difficult task.
What's often needed is an explanation to go with the diagram. As a simple example, take the Ford electronic throttle control; I struggled for a while, until I found out Ford use both an analogue and a digital signal from the pedal. Just looking at the diagram doesn't tell you this. If you don't know what to expect, and an output or input is missing, you can't make an accurate diagnosis.