speakers do not have to be wired correctly...they will just be out of phase if wired improperly.

I believe if you are running them off your headunit it is possible that those channels have gone out on the internal amp of deck. If you have a multimeter, check the ohm reading from the wiring harness of the radio to the speakers, and then pull the speakers and directly check the ohm load at the speakers to see if they are blown. You can also use a 9V battery or tone generator to check if they are blown

And just to clarify one more time, you can wire them incorrectly and they will still play, but will be out of phase unless you have all of them wired incorrectly and then technically they are in phase w/ each other and would sound fine.