I think you are looking at this like basic household wiring.
Sorry to say it's not that simple! There are no magic glasses to give you x-ray vision like Superman to visualize the flow of the electrons thought the system ;-}
While one can use the swap out method (swapping out with known good parts until something works). This gets expensive and you have to have the right parts for the given system to start with.
Even using DVM's or an oscilloscope have there limits without having a circuit & layout diagrams to work off of won't get you far either.
Often one has clues (symptoms) that can lead to a direction as well as experience working on many systems that can make quick work in diagnosing a problem.
As you didn't give us anything to work off of here, you may find finding someone in your area who has the skills & tools to figure out whats happening with your system a cheaper and safer path in getting your system up and running.