2005 impala special stereo harness

I would like to intall a after market stereo on a 2005 impala with no on star.  It just has a basic cassette player.  I went to a couple of stores and they said I need a special harness.  that costs over $100.Something about its a special harness.  Is this true?  Thanks

We sell that harness for 100 dollars.  The chime that you hear when you leave the key in the ignition, and for other things, that noise comes out of the drivers door speaker.  If you replace the radio you lose the chime.  Also there is no switched 12 volt wire in your car's harness.  The car's computer tells the radio when to come on.  This special harness gives you a switched 12 volt and provides a speaker so you do not lose the chimes.  You are one of the lucky ones, the OnStar harness is 150 bucks and the OnStar Bose unit is 170 or so.

thanks for the info.  You mentioned "we sell" , do you know where I could get that part?

thanks.