Here's a question for audio experts, one which I'm embarrassed about as I've done lot of work using and even building audio equipment too. I recently put my original pioneer sound (head unit) system back in my car. This system has 4 speaker outputs for front, rear, left and right. All the outputs have two wires, so if there are any electrically 'common" connections you can't tell by looking. All the wires from the audio output plug are color coded. To help avoid errors each channel has a pair with a color for the + side of its speaker, and the same color with a black stripe for the - side.