On my Ford, I can't have the interior trailer lights on without the truck running. It sucks. I reorganize and clean up things in the dark. I'm wanting to get a deep cycle battery and feed it into the switch so I can have lights regardless of trailer power. No clue how to do this. I have been told before to take the positive wire and splice it into the white trailer wiring, then the negative post just ground to the frame. Looking for it to automatically recharge (if possible) while the trailer is plugged into the truck. Anyone have any info / ideas?