Replaced radio: port side no power. Need help tracing red wire

[Robin226]

2001 226
Sony for Sony. All is working except port side speakers. No power to port side red wire.

Need a wiring diagram or help on how to trace and where the wire is. Maybe corrosion?

[Big Block Power]

Cobalt stereo wiring is horrible. Sorry they tied so many things together it was easier to just run new ones.