System Schematic Basics The system schematic is used to illustrate the electrical components (e.g. ECUs, sensors or switches) in a vehicle electrical system and their connections to each other on an electrological level without physical realization details. In many companies the system schematic is specific for an individual system and not an individual vehicle variant. The example below shows such a system schematic with four components (MX1.1, MX3.1, MX3.2 and E1.