In addition to the other responses, if you’re bridging the amp, it acts like a differentially balanced amp so you can’t connect up the black wire to the black post as it’s not a ground but rather an additional hot supply. You’ll need to ground to the chassis or some other secondary ground.

This

How do I stop my subwoofer from humming? Watch the above post.

Once you've solved the ground issue, trim the cable(s). They are not well shielded.

Better yet, buy these. I had them terminated with spades and I did not need the black "ground" wire but you can also order a 3 wire version, and only one if you dont need a stereo pair. These are FAR better than stock and cheaper then the REL blue wire or even SignalCable.com