My new trailer has a provision to power the 12V lights from the tow vehicle as long as its connected to electrical plug on the hitch. It will also charge the battery in the trailer while you're driving. The trouble is that my tow mule doesn't have the accessory wire in the plug connected. Anyone know where the source for the constant 12V feed is connected on their tow trucks? I'd like to hook this up, but need to know where it's connected. Thanks.