do some temporary wiring.
connect a jumper from a flat four plug at the tow vehicle on the ground wire to the trailer ground.
put your vehicle park lights on, and connect the brown from the Tow to one of the green wires at the tongue with a jumper, and go to the back , see which light
comes on. Mark the wire with a piece of masking tape and move on too the next wire. when you have all the wires tested, you can join the running lights together, and leave the signal/brakes separate and connect to a new flat four plug. Then off you go!