Check the right wire. Go from the deck and check the wire all the way to the speaker. If it's frayed, broken (melted even) then replace it. Also take a 9v battery to the leads on the speaker (while unplugged). If the speaker doesn't make a popping sound, then it's fried. Go to a junk yard or something and get another. Like the other guy said, check the balance (or if someone hooked it up wrong, check the fade)