I saw you had a previous regarding this as well. For a subwoofer, you can either use a mono or 2 channel amp. To get the signal to the amp, as el_duderino stated, if the amp you purchase has high-level (speaker level) inputs, you can tap the rear speaker wires and connect them directly to the amp. If the amp does not, you need an LOC (line-out convertor). As for power and ground, those were addressed in your last post as well. Straight from the battery by the spare tire and ground using a bolt near the spare as well (scrap some paint away if painted surface).