I spliced into the factory harness because I was still going to use the factory stereo. Crutchfield sells the adapter harness to plug into the factory harness for an aftermarket stereo, but not the plug to plug back into the factory stereo. I could not find a plug that would fit the Outback's stereo, and to buy another wiring harness for the Outback would have been $200. So I spliced.

I made sure that my splices would not affect the car, though. I soldered every splice, and used 1/4" insulated plug adapters to hook into the Empeg's harness. I wanted to make sure that I can still sell the car later

I don't have the alternator whine like you guys do because I am using an FM Modulator and the factory head unit. As for the amp trigger, I am using the blue Empeg wire (amp turn-on) to trigger a relay that switches on the FM Modulator. Isn't the blue wire to trigger the amp and use the RCA outputs?