Controller won't show charge with coach battery's connected.

I am installing an 18 watt solar panel to maintain batteries while in storage, etc. All wiring was done correctly with polarity confirmed. When I tried to hooked up controller it did not show charge. After much personal conversation, I disconnected the coach batteries from the trailer and hooked up the controller. It is now showing charge. and is charging the batteries.



I have no issues with trailer that would indicate a wiring issue. IT is a 2014 FC 30 foot Twin bed.



What is going on???