To resolve the issue of your Enbrighten lights not lighting up after connecting up to three strings, follow these actionable steps:

1. Inspect Connections:
Ensure all connections between the string lights and the power source are secure. Check that no connections are damaged. Sometimes, loose or damaged connectors can prevent the lights from functioning correctly - learn more.

2. Power Cycle the Strings:
Disconnect the power to your lights for about 30 seconds, then reapply power. This may reset the system and help the lights recognize the additional strings - learn more.

3. Check for Pairing Issues:
If the lights are smart Wi-Fi enabled, ensure that they are correctly paired by pressing and holding the power button on the remote within 8 seconds to sync the lights with the remote. The lights should blink to confirm they are connected - learn more.

4. Test Each String Individually:
Disconnect the last string that is connected and test each string one at a time by plugging them in. This will help identify if one string is malfunctioning or causing an issue when connected in series - learn more.

5. Limit the Number of Strings:
Ensure you're not exceeding the maximum number of strings that can be connected. For many Enbrighten lights, the limit is often specified in the product manual or specifications (usually up to three to five strings, depending on the model). Review your product information for specifics - learn more.

6. Contact Support if Problems Persist:
If you’ve followed these steps and the lights still do not work, consider reaching out to Enbrighten customer support for troubleshooting. They can offer specific guidance based on your model and issue.

By following these steps, you should be able to diagnose and potentially fix the issue with your Enbrighten lights.