Another potential consideration would be the relay grounding, which is commonly tied to a function such as Fuel Pump output, in order to prevent the devices (injectors, coils, etc) from receiving power except when the ECM commands and is ready to control them. While not universal and much depends on actual power flows and defaults, a scheme such as this prevents injectors flowing without control, coils with runaway dwell, devices back-feeding power to the ECM, etc.
This is another instance of "opening a can of worms", involving other considerations into a basic concept diagram. Perhaps just a note, or dashed optional grounding path "to ECM" or something? Something that indicates there's more to consider, but in the diagram isn't the place to get into it.
Likewise, most systems do not take power from the key switch, but Main Relay power or distribution point switched by the key. A more generic "Switched +12V" power source is often used. Your call on whether to imply power and ground should be directly from the battery or other controlled source.