I installed my Mazda OEM harness last night. No big problem except I had to cut the grommet to get the Keyless Entry wire in. The Keyless wire was not really a problem but I had another wire with a rather large connector that would not fit through the grommet. I don't know what it was for...
Thanks for the information. I have ordered a Draw-Tite hitch and have been having trouble finding the OEM Mazda harness for my 2013. I will check this out.