I have not been able to find any wiring diagrams our forum discussion which state explicitly what the third wire (yellow/gray) is for. I tested the wire of power ,,, none. I tested to provide a ground ... light would not function. Since the new license plate light integrated with the AVIN backup camera only has a power and ground wire, I have connected those and the light works properly. I will just tap off the extra wire and put the trunk handle assembly back together.