I am having an issue with my Garmin GDU375. It has an error message of "Not Receiving External GPS RS-232 Data Using Internal GPS flight plan for navigation"

I have tried replacing the GPS antenna. The Trutrac autopilot is also displaying a NO GPS SIGNAL. I assume since the GDU 375 is using internal vs external antenna.

The internal GPS works well, just have lost capabilities.

Any thoughts or ideas?

Jeff Mickler