I converted my trailer over from the 6way plug to the 7way RV style to match the truck. Lights and brakes work as they should. The black wire from the truck has power when the truck is running. I think its for the break-away brake battery, but would like confirmation. The trailer does not have the charger for the battery and I assume I'll need that and cannot hook the black wire directly to the battery. Please steer me in the right direction.