I ordered a set of LED trailer lights from Amazon. They were obviously mailed from China and each unit has three wires from the back; black, red and green. I double checked with them by Email and here are the wiring specifics. The black is the ground. The red is for the turn light/ brake light. The green is for taillight which illuminates when the vehicle lights are on.
Soooo, for a normal North American boat trailer harness this what worked for me:
Rear Left light
Black to ground or to white ground wire from harness
Red to yellow from harness
Green to Brown from harness
Rear Right Light
Black to ground or to white ground from harness
Red to green from harness
Green to brown from harness
Works fine. Here is a pic. PS. No moaning about Amazon please. There are other postings for that. Thanks.