Before the fall in gas prices, I drove a lot of miles, and rarely used the Heat and Defroster. I typically seen voltages of 13.9-14.5. Within the last 6 months, I've been driving the car for comfort like a normal person would. Heat, Defrost, and heated seats. And I've noticed the higher winter voltages.
When using the remote start the rear window defog comes on. This is tied into outdoor temperature. I'm not a fan of this, and that could be another reason why the voltage is going high. Make sure when you get into the car you shut the back window off.
I used the console ground, because it was there, and I've had nearly all that apart allready.
I briefly looked for a ground by pulling up the drivers door bottom door sill on the inside. I thought I remember reading something that there's a ground post there.
There's another ground behind the radio, based on info when I was looking for the console ground. I didn't think that was convenient at all.
What kind of mats did you buy? The generic ones off "the bay" or something else? Mine were white with an actual wire in them. Not the carbon fiber ones. I feel I paid a little too much, but honestly I'm not sure that I want to do the job again. Even the second seat took two good afternoons to remove from car, un-upholster, heat, and reinstall.
I wish the pads I used were a little longer. I'd really like a pad big enough to cover the entire back of the backseat, all the way to the shoulder area.
Anyway it works. I may plug the heated seats back in, as I see the voltages are back at 14.9-15.0 today, and actually I'd expect lower based on my first 3 years of driving.