Hello Charley and Dionne - welcome to the forum!
I moved your question to a more appropriate section and used it to start a new thread, because it had no relationship to the thread you posted in.
I'm having a bit of trouble understanding your question, blame it on my advanced age (84 years old). Are you saying that there are two batteries in your trailer but only one is connected to anything? Is the solar panel one of the optional ones that came on some HiLos that was supposed to help charge the installed battery? If it is that solar panel, then turning the switch on should help to maintain the battery that is connected, but it won't do much else - the output of the panel is only 15 Watts.
- Jack