Old time distributors and carburetors didn’t care how badly you wired the electrical system.  Digital systems are not so forgiving of poor wiring practices.  Noisy power or ground wiring is one of the most common causes of initial builder problems with computerized equipment (including ECUs). 

In addition to the wire bundling answers you got, the basic power wiring is as or even more important.  Here is a basic aircraft wiring scheme that I recommend in latest version of the installation guide.  Not detailed but somewhere to start.  Note the independent power feeds from the battery for the various systems.  This is a physical as well as electrical representation.

Tracy