I have a 2dr 2004 Chevy Cavalier. I bought a new stereo for it. I couldnt find the right stereo harness so I decided to go with out it.So I indivually connected all the wires using a wire diagram and with shrink tubing. After I was done I realized it wasnt working. The stereo has power the display flashes red and so does the backlight. So what could I have messed up?