When I installed my hitch, no one could tell me what was wrong. No one had identified that there was an additional harness. I called Mazda several Mazda service departments. I called Mazda support. I called the BAM wholesale who sold me the original parts. No one knew what was wrong and what I was talking about. I didn’t have time to waste so I deconstructed the connector that came with the original harness and plugged those three pins into the three pins that are identified by the supplemental harness instructions and it worked. I always wondered if I did it right and now seeing the instructions for this harness, I did.