The brake circuit of the Tekonsha Prodigy P3 # 90195 is on a different circuit than the lights for your trailer which is why everything else it working great but the controller is having issues.
Since your note is saying that the trailer isn't connected you need to check the blue wire from the controller to make sure it's running without any issues to the back of your motorhome. You likely have this wire damaged, pinched, or exposed somewhere which is causing a misreading. If you can't... view full answer...