My recollection is (presuming you have all the correct wires), there is a DIN wire that plugs into the bass module. The other end of that is connected to the speaker with the volume control on it and another wire goes from same speaker over to the left speaker.
In other words, I'm not sure it's possible to wire it up WRONG, again, presuming you have the proper wires for it.
Maybe someone will correct me if I'm wrong?
Professor Thump told me to take a Custom 3 and stick it in my ear. I did...and it sounded great!!!