The Sega amps are only 4 ohm capable. If you are using standard car audio 4 ohm speakers, these need to be wired in series. Do not just run the wires also over to the new speaker. If you do that you will be putting too much strain and heat on the audio amp and will blow it eventually if not soon. The proper way to wire these in series would be to desolder and move the - wire from the original speaker to the - on the new speaker. Then run a new wire from the - on the original to the + on the new speaker. Now everything is wired safely.