If you're looking to get a surround-sound effect from your car stereo then wiring two rear car speakers will do the job. For extra effect you could also wire a subwoofer. Most car stereos and speakers have RCA sockets that make wiring easy. You need to check that your car stereo has extra unused RCA sockets to support the addition of rear car speakers.
Measure the distance from your stereo to your rear car speakers. Remember to take account of where the wire will be placed as it needs to run under carpets or door sills so it's hidden.
Purchase two ready-made RCA wires of suitable length. Always allow a little extra as wiring rear car speakers can use a lot of wire: you can always tie up extra wire. RCA wires can be purchased from most electrical stores. They are inexpensive and available in varying lengths.
Remove your car stereo, if you haven't already, ensuring you first disconnect the power supply.
Feed the two RCA cables through from the back of where the car stereo is located. Leave enough wire protruding to ensure you can easily connect the wire to the sockets.
Lay each wire along the car to get an idea of the best way to fit it. Position each wire under the carpet or behind the plastic seals near the car floor. Carpets often unclip so running the wire beneath the carpet may be easier than removing the door sills
Feed the wires through to the rear of your car, ensuring that you have enough loose wire to connect each speaker.
Push the RCA plug on the end of each wire into the rear speaker sockets. Check to make sure they fit firmly.
Plug the right speaker wire into the car stereo socket market RR (rear right) or similar. Repeat the process for the left speaker.
Reconnect the power to your car stereo and turn it on. Check that each speaker is working then turn off your car stereo.
Replace your car stereo then turn it on again to ensure that all the speakers are still connected.