Basically you have to splice into left and right to get a full signal.. That's because your HU is running in stereo.

How are you supposed to splice into both if you have one wire? Can somebody please look at the sub I'm looking at?

Ive looked at your sub.. Did you buy this new? Do you have all the install hardware? What color is this one wire you are talking about?

I haven't bought it yet. And there is a harness that comes with, and it included the power wire, ground wire, signal input wire, and I think another one for the remote turn on but I'm not sure. I'm going to talk to crutchfield sometime and try and get some info. But please explain on how people have spliced a powered sub into the factory rear speakers.

PM sent to the OP