2004 GC towing - wiring

I am planning to install a hitch to tow a boat, and have heard that there may be a wiring harness hidden somewhere in the rear of the vehicle that I will tie in to. Could someone tell me where to look for this? Thanks for your help!

Inside left rear cargo bay underneath carpet

I am planning to install a hitch to tow a boat, and have heard that there may be a wiring harness hidden somewhere in the rear of the vehicle that I will tie in to. Could someone tell me where to look for this? Thanks for your help!
I don't think there is wiring harness unless it came from the factory with the Trailer Tow Group or Trailer Tow Prep Group option.