Hello@Will_U ,

Thanks for contacting our community.

May I know what the model number of your device is? Please refer to

How to find the model number of your TP-Link device 

How to find the hardware version on a TP-Link device

This usually happens because powerline adapters rely on your home's electrical wiring to transmit data. If the outbuilding is on a different electrical circuit, or if there is increased electrical interference or distance, the adapters may not be able to communicate, causing the powerline light to turn off.

Here are some steps you can try:
1. Plug the powerline adapters directly into wall sockets instead of using power strips, surge protectors, or extension cords, as these can block the powerline signal.
2. Check if the outbuilding is on the same electrical circuit as your main house. Powerline adapters may not work across different circuits or separate breaker panels.
3. Keep the adapter away from high-powered appliances (like air conditioners, washing machines, or power tools) that can cause electrical noise and interfere with the signal.
4. Move the adapter to a different outlet in the outbuilding to see if another location provides a better connection.
5. Update the firmware of your powerline devices to the latest version by following this guide: How to upgrade firmware of TP-Link Powerline Adapter?