IF you decided to go with tapping the rear speaker wires, I can try to help you out since that had been done to my SVT before i got it. (since then i reconnected the rear speakers and fixed things up a bit) the rear speaker wires were tapped in the B-pillar. It comes off with a few screws and a bit of fighting. i dont remember the exact color of the wires, but they are bundled up with the rest of them. check the ones coming out of your HU/Wire-Harness/Factory Amp (depending on your setup) for the colors. you can tap them here and run them down under the rear door sills to the trunk. (you have to tap them here because they go into the door after that point).
i dont know if that helps.
