You should always make sure you have the correct polarity when hooking up speakers. The aftermarket speaker wiring harness will have a stripe on each of the white, grey, purple, and green wire along with one without a stripe. The stripe indicates the negative wire and the wire without the stripe indicates the positive wire. Speakers are mechanical cones that push and pull air to create sound. Sound pressure and vacuum is created by the speaker either pushing out (pressure) and pulling in (vacuum). If you reverse the polarity on the right side from the left, one side will be pulling air in and the other will be pushing, which will diminish bass. The sound will be very poor.