I think you're on the right track.
The wire harness on the left is for non-premium, ford applications. The left one is for speakers. The one on the right, is the one you will use for the 12v, ground, dimmer(if available), and so on. The wire harness on the left is for the non-premium guys (not that they're missing much)
The premium amp... YAY... The connector on the left, is the one where the speaker outputs are. The connector on the right is for signal (Preouts). You want to plug the speaker wires (not preouts) into this plug (in their appropriate location). When I "plugged" mine into the plug, they were pretty snug. I wrapped each pair of wires with electrical tape by the ends to keep them from coming out and then wrapped the tape around all of the wires. (I can take a picture of that tomorrow if you want) Some of the wires, I had to re-tin because they were too thick to fit in the plug without damaging it.
This cable allows you to use the premium amp. (and not use the amp in your head unit, although the amp in your pioneer HU is more than likely better than the ford amp)
This make sense?
