1990PORSCHE928GT

Does anyone out there have a wiring diagram for the CD-2 RADIO that is the stock CD/Radio in a '90 928 GT?? Don't have full sound on the left side of the car and need an audio guy to take a look at it.

Or, does anyone know of a Stereo guy, or an Audio Company, Best Buy, etc that could look at the stereo and diagnose and fix it?? I am in the Chicagoland area.

Thanks to All!!