Where is the factory towing package wiring harness grounded to? I'm referring to the harness that my brake controller plugs into under the dash. Am I correct that the most reliable design is to ground to the battery?

 

Not necessarily.. grounding it to a sturdy peice of metal will work too.. but its already grounded if you have the factory towing package with the brake controller harness...
Scott

 

I had the tow package wiring harness installed in my truck a month or so ago, it's grounded to the battery in the front of the rig and to the frame on the rear of the truck. As DieselJunkie said, if your truck came with the factory tow package all you do is plug your brake controller in(blue female plug under drivers side dash, fare left) and go.