System activity and status can be determined through the activity of the LEDs on the switch. The status LEDs can display solid amber or flash during boot, POST, or other diagnostic tests. The CPU and the I/O modules use LEDs to provide information about either the operational status of the module or the I/O. By understanding what each symbol represents, you can decipher the connections and relationships between different components in a circuit. System is operating normally without alarms. The following table describes the LED indicators when two power supplies. After switching on, the Bus Coupler immediately checks the connected configuration. In this guide, you will learn: ► How to identify common.