Quoted from Oldgoat:Here was the epiphany for me, thanks to a comment by a Pinsider, : the schematic is a logical representation of the game at a given point in time (e.g., coin dropped, credit button pressed, game at ball one ready to play), not a physical wiring diagram. So you can't look at the schematic and think...ah ha, there is a wire that goes directly from this switch to this coil. Now mind you, I still suck at reading them; however, that little nugget helped a ton and eliminated a lot of frustration.
Please note this important addition, it makes a difference when you are looking at things trying to sort them out:
coin dropped, credit button pressed, game at ball one ready to play, POWER TURNED OFF.
Also, there can be inconsistencies within the schematic concerning this state, but they usually are minor. For example, on the Bally Bon Voyage the ball count unit disc is shown pointing at 1. This doesn't make sense given the above, it should be pointed at 5 which would match up with the balls per game adjustment plug as it is drawn (this is an add-a-ball so you start with the # of balls remaining rather than the ball in play). Its a minor thing but still disagrees with my OCD nature.
There can also be errors in the schematics. For example in the Bally Bon Voyage there are 2 switches with the same designation, one of them was mislabeled. That is one of several errors in that schematic. This can drive you crazy if you happen to be trying to work on that specific part.