If you've ever looked under a layout, the maze of wires could lead a person to think that the wiring is much more complex than it actually is. What appears to be a spider web of wire, in reality are the same basic connections repeated over and over dozens, perhaps hundreds have times.
There are really only two basic circuits on most layouts:
 | -The one that runs the trains the Track Power System. |
| -Optionally, a second circuit that runs everything else. By everything else I mean: switch machines, crossing signals, structure lighting etc. This is the Accessory Power System. |
These two systems are totally independent and in no way connected to one another.
Certainly, there will always be the individual with a more sophisticated situation. However, for the overwhelming majority of layouts this is all there is. In fact, in many cases you only need the track power system.
