odd...generally - there are three connectors on that amp plate ---
- one from the antenna
- one from the external connector
- one to the bedroom connector
When you turn the amp off, it should take a signal from the outside external connector and pipe it through the trailer. If you have not used the external connector much - it might have some corrosion or rust in the connector. Try taking a small piece of wire and work it in and out of the external connector and clean it off a bit.