Originally Posted by caper
I would also be adding a battery isolator if you do not already have one.
Good call! However, it may or may not be necessary.
On my tow-vehicle, the battery charge pin of the seven-way plug is not "hot" unless the engine is running.
Based on that, I do not need an additional battery isolator.
The relay involved acts to prevent the TV batteries being discharged by the trailer's systems.
Of course, the O/P's Windstar may not have that relay already installed, and is well-advised to add one.