US manufactured vehicles use a standard system that shares the turn signals and brake lights. Hence 4 wire connector. Asian vehicles use a standard system where the brake lights and turn signals use separate lights and wires. Hence 5 wire connector. Other needs such as cabin power and electric brakes may be run through additional wires. 6,7 or 8 pin connectors
I could have adapted to the 4 wire setup using some diodes. But I chose to go ahead and add some led brake lights to the trailer. I will then use the 5 wire Asian type set up that matches my bike. I can then tow the trailer with Asian vehicles such as Toyota, Honda, Mazda, Hyundai etc. without modification. Also since the 4 wire lights will still be on the trailer I can simply make an adapter so the trailer can be pulled with a vehicle using that setup. No diodes needed.
I wanted to know the standard pin locations so I wouldn't need to be tracing wires every time I made a vehicle change.
Mike