Control Relay: Description
WARNING: This page is about a different car, the 2004 Kia Amanti. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is turned on, battery voltage is applied from the ignition switch to the ECU, turning ON the ignition power transistor and energizing the MFI control relay coil. This turns ON the MFI control relay switch, and supplies power from the battery to the ECU through the MFI control relay switch.
WARNING:
When inspect the control relay, connect the battery voltage to the exact terminal. If not, control relay may be damaged.