How to install a radio in a 94 saturn?

iv gone back to the store three time to get three different radios and all have no audio. all wires are connected securly, but on the original radio plug there were 2 extra wires, a brown and a gray, that according to the wiring schematic, was for exterior and interior lights. wtf is that about???? i cant get any sound out of after market radios, but the stock one works, so what are the other 2 wires for and how do i hook this up so i have sound without re-wireing the entire car?|||Try this in the back the factory harnes i thing is a white wire to turn you amp on the wire is not in the harnes you plug just put the remote wire blue/white to the white and i thing will work