Greetings!
This is most likely an internal radio issue, not something external like a wiring connector.
To have this repaired, you will need to remove the unit and send it in to a Delco service center for repair.
Here is a link to one of the largest AC-Delco service centers on the east coast that the dealers use for these repairs. They can usually quote you a flat rate price over the phone for repair before you send the unit in for service. By sending it in yourself, you save the price markup charged by the dealer or aftermarket repair shop...
Click here for service center contact information:
http://198.66.219.68/YourServiceCenter/contact.html
I hope this is helpful to you; if so, an accept would be most appreciated! thanks!