Replying to your post - that's great information. We were supplied with everything from a supposed LS Swap person. He has provided some technical assistance trying to help but he is to the point he has no idea. That's where we are at. We have done 4 of these LS swaps with no issues on the 4 - until this one.... Nothing makes sense that is happening. It's a stand alone harness that was sent with the PCM/tune from this individual. You are correct, I do not understand what's going on. No disputing that. That's why I'm here asking the question. You might have helped solve it. Part number on the ECM is 12614085 which has 1 black and 1 grey plug