Those LED lights on your TU-500 and TU-600 lets you know the status of you GPS connection and connectivity. 
In this diagram, you’ll find the information.
For more details, please follow this link from our Installation Guides https://content.trackunit.com/hubfs/PDF%20Assets/Installation%20Guides/Trackunit%20%7C%20Installation%20TU600%20%7C%20EN.pdf?_ga=2.141919666.1828221907.1652085141-1508351258.1642617223
And from our Help Center as well 
https://helpcenter.trackunit.com/s/article/What-do-the-LED-status-indicators-on-Trackunit-Raw-mean?language=en_US