Hopefully, I can explain this to get an answer. I took my 2007 Hummer H3 for inspection and when the inspection macking was plugged in the message came up that it had power but couldn't link up. They tried a handheld machine and everything worked fine but every time they plugged it into the computer it had the same message. I'm trying to find a schematic of the plug in the car. I am not the original owner but when I took the plug down there were 4 wires. I thought that the hot wire was the only thing running to the plug but it looks like someone might have spliced a wire into the hot and run it up to some kind of cluster box for something else. If anyone can help with either a schematic or some info on this it will be appreciated. I hope I was able to explain what I was looking for. Thanks

 

Follow link and scroll down. PDF of wiring and the rest of repair manuals for free.
https://schwarttzy.com/h3-hummer/