This is for your information. I could not find a diagram like this so I pulled the doors off one by one and chased the wires down through continuity. I did the same to the back of the stereo. This helps with the hum or whine or whining that happens with these after an aftermarket stereo is installed...

This is an FYI for the community on changing the downstream O2 sensor. There is nothing out there that I could find about the 2003 model. There is a video for the 2005 model which has the pig tail location under the dash. After pulling the carpet up and finding nothing, I scoped the body hole to see...