Harness for truck to rear trailer plug

[brainpause]

My truck is 2002 GMC Sierra 2500HD. It has UY7 RPO code. It has a harness, but some wiring genius screwed it up, long story short. I want to start fresh, and just replace the whole darn thing from truck to plug.

 

I have found harnesses for UY2 RPO code, but not sure if they are the same. Some of the reviews say it was "the wrong one", but don't mention why.

 

Can anyone direct me to the correct part number?

 

Larry