Today's complex automotive engines need information regarding temperature, fuel consumption, speed and pollution to operate properly. The instrument making these decisions, the Engine Control Module (ECM), needs power to operate the same as any other electronic device.
The Engine Control Module in any automobile receives signals from various sensors throughout the vehicle to monitor engine performance. If a threatening situation occurs, the ECM sends a signal to operate a "Check Engine" light.
The ECM Wiring
Wiring comes to the ECM from various sensors but also sends signals to other devices. The fuel pump, along with several other critical parts, operates on signals from the ECM.
The ECM Wiring Relay
The ECM wiring relay provides battery voltage to the main input wire to the ECM, just like the power cord to a computer. The relay closes when you turn on the ignition.