Usually, TP-LINK powerline adapters have three LED lights:
1) First one stands for power;
2) Second one stands for powerline connection;
3) Third one stands for Ethernet connection.
It should be on all the time. If it is off, please change a socket to have a try. If still can’t power on, please arrange to exchange a new one.
When it is in the pairing procedure or in power-save mode, the Power LED will flash. After the process is over, the Power LED will back to steady on. About how to pair them, please refer to the FAQ below:
After you have successfully made the powerline connection, the Powerline LED will be on. And when there is data transfer, the LED will flash. It will be off when it is in Power-save mode.
For TL-PA511/TL-PA551, there are three colors for this light.
When any device is connected to the Ethernet port and be powered on, the Ethernet LED will be on. It will flash with data transfer. Only when the LED is off more than 5 minutes, it will be in power-save mode.