Audio Systems: extra set of speakers, internal amplifier, speaker switch

Question
We have a Sharp mini component system.  The house has wiring that runs from the LR to a set of speakers on the screened porch.  We would like to hook up this system to those speakers.  There is only one set of jacks on the back of the stereo.  I have been told that I should get a "speaker switch" in order to do this??  Also, the wire in the wall are not color coded.  Can this be done?

Answer
Does the mini component system come with speakers? If so you will need an impedance matching switch because those systems have been designed only to work with 2 speakers. If you hook 2 speakers across one set of terminals you may damage the internal amplifier. Radio Shack is a good source for peripherals.