When it comes time to add a subwoofer, it is often very easy to wire the rear speakers of a vehicle's stereo to the terminals on the subwoofer. The process of rerouting the wiring to address the rears and the subwoofer is often logical, because both types of speakers are generally tasked with handling bass frequencies. Using the existing wiring means less installation time and quicker enjoyment of the sound system.
Cut a length of speaker wire sufficient to reach from the subwoofer to the rear speaker wires.
Snap on T-tap connectors in on a section of the left rear speaker wire, closest to the speaker's positive terminal. Secure the tap with the crimp tool. Repeat this process for the right speaker's negative wire.
Strip 1/4 inch of insulation from the end of the speaker wire leading from the subwoofer. Crimp on a male spade connector to the positive speaker lead on this wire. Do likewise for the negative lead.
Route the subwoofer's speaker wire to the T-tap connectors, keeping away from traffic areas or potential damage. Push in each male connector into the corresponding T-taps until they snap into place.
Make the appropriate connection at the subwoofer's terminals. It is imperative that the polarity observed at the rear speaker terminals is duplicated at the subwoofer terminals, or the system will be in series, reducing bass response.
Another term for T-tap connectors is Scotch lock, although many manufacturers make them as a standard electrical connector.
Always perform speaker wire connections with the stereo off.