Question for newer Lance owners that added solar-

A voltmeter should reveal what that wire is carrying.

I would contact Lance for that if it is not covered in manual.
Over the years the designs are changing and sometimes the solar is connected directly to the battery, sometimes it taps before disconnect switch.
My 2002 Lance has factory solar and I see some kind of electronic board in the circuit.
It works, so never investigated what that assumed controlled does, but adding to the system calls for checking it all.