Strange stereo sound issue after re-installing AVIC-F7010BT

[PeterPan]

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.

Since this system had been in the car in the past, I thought it would be easy because of the color coding on the existing connector plug and the existing speaker wires. So I did a basic sound check before assembling it all, and all the speakers seemed to be working. But after listening to for a while, I realized the stereo has a very strange sound. All parts of the music where the stereo separation is obvious seem to be at normal volume and seems correctly separated, left and right.  But any sound that is intended to come mainly from just one channel is exceptionally loud! Also, music elements like the vocals which should be in the center are subdued and hard to hear.  This is true even with the doors open, so I don't think its a matter of accidentally wiring the speakers out of phase. But I do think I may have made a wiring error. The front left channel wires are white and white-black, while the right channel wires are gray and gray-black.  I do remember noticing that the difference between the white and gray wires was not as obvious as I'd like but i thought I got it right. But if I somehow did mix up two of the front left/right speaker wires, could this cause the cancellation of center audio, and over emphasis of the stereo separated sounds I've described?

I'm asking because I'm not really sure. The sound system does have balance as well as front/back fader controls, and when I tried setting the audio completely left or right, the sound is indeed directed to just that side.  Would that still be true if mis-wired the speakers as I described? Or could it be an actual internal defect inside the head unit (like a couple of speaker connections becoming internally shorted maybe?). Unfortunately as with many cars, taking it all out to recheck all the wiring is going to be a pain to do. So I figured I'd ask whether my theory even seems plausible, or if not what else am I failing to consider.