I installed the rear mounted sub with the built in amplifier in my XP 1000. I had to cut the plug off that has the blue, red, white, and black wires (these are not the main power and ground). I have a Bluetooth unit running to an Alpine amp through RCAs. I assume the blue wire is the remote turn on for the sub amp, but how and where do I run the remaining red white and black. I bought a couple of RCA y’s and tried to rig it with no success.