The dealership I went to didn't even look under the hood, just asked me what wasn't working right and then basically said "You can pay for it to be done and then if we find anything wrong, you can get your money back."

Forget that.

I'm half-tempted to just leave it be, and if/when problems crop up that can be traced to the harness, using that as my reason to go buy a new car.

"Think of it, if you like, as a librarian with a G-string under the tweed." Clarkson on the Mondeo.