Six months ago, I did the big 3 with Knu 1/0 wire, and put a HC600 in the trunk. My voltage would idle right about 14v, and with 1kw drop to ~13.4v. I ended up selling my subs/amp at that point, and got new stuff, and was only running ~300w for the last 5 months.
A couple weeks ago the wire I added from my alt to the battery fell out of the terminal at the alt, and melted against the heat shield. Took that off a couple days ago, and re-measured 13.85v idle.
Got new wire from Knu today and redid the alt wire. When I measured the voltage now, it was 13.25v at idle, with the stereo, amps, AC, etc.. off. Turned on the AC, and saw it dip down to 12.8v then quickly went back up.
Could it possibly be due to the heat? Its one of those days that the socket burned my hand after sitting out for the two minutes it took for me to route the wire.