One of our trailers is an Interstate Cargo trailer. I need to install a battery inside the trailer so we can have interior lights when the truck is not hooked up to the trailer. I want to wire it such that the truck will re-charge the battery when in tow. fyi...Currenty, you have to have the key ON in the truck to run the interior lights in the trailer. it does not matter if the truck's running lights are on or not. I hope that helps explain the current wiring situation. appreciate any advice on how to wire this up correctly. thanks.