Hi, we have a trailer at work a large car transport trailer. All the lights suddenly stop working, tested electrics on the van with a lighting board, all working perfectly. When I connect a wire to the white wires in the plug, and the other end to the bare metal on the tow bar on the van, they work. Rang the manufactures of the trailer, they sad there is no ground connection to the trailer chassis because it's not needed with that loom aparently . Any advice would be appreciated! Thanks