Does the wiring harness adapter have the same color wires coming out of it as going in on the other side?
Do you have a diagram of the wires for the Alero? If you don't, that is your problem....you can't just attach the same color wire from the adapter to the same color on the new radio......
Your original radio has two possible configurations.....one with an external amplifier, one without...
I went to Crutchfield.....that model is discontinued....but I checked to see if that model fit......only option was whether it had Onstar or not....tried both, said it would not fit....