All you need to do to hook up the sub is take the blue wire with the yellow stripe located in the factory wiring harness and hook it to any +12v source coming from the radio that's only on when the ignition switch is "ON" (i.e. blue amp remote wire, power antenna lead from aftermarket radio, etc.)
The factory sub is not a powerhouse, but it's better than nothing. It doesn't sound too bad if it's still in good shape.
