Gene,
not trying to be a downer, but don't get your hopes up too high. You certainly will not get a new car. I don't think you will get very much from court, except maybe a refund on the harness. The stereo works. They did not break anything on your car per say, as it all works. You are perceiving a problem in the future, but none is there now. That is how the judge will see it if you take them to small claims court. That is where it will end up. Maybe take this as a lesson learned, notify BBB and or other consumer advocates online...and live with it. Getting an ulcer and spending time and blood pressure on this may not be worth it in the end.