The -12V rail is pretty much obsolete now and is only kept on to provide backward compatibility with older hardware. Some older types of serial port circuits required both -12V and +12V voltages, but since almost no one except industrial users use serial ports anymore you as a typical home user can pretty much disregard this rail.
I'm running a thermaltake 430w on a gigabyte 970-d3 board with an AMD FX-4170 processor. So I'm guessing that I'm not using the -12v??, so why is it fluctuating? Which one is the -12v? I also noticed my processor voltage was ranging from .9v to 1.44v. At first I thought this had to do with the -12v, but I'm starting to wonder if its just the way the architecture of the processors handles loads. My phenom II doesn't do that.