It is important to have a diagram to use as a guide when making changes to a car. A free wiring diagram can be found in the cars maintenance manual, or possibly at as a print out from an auto part store.
You can find a 1999 Chevrolet Corvette radio wiring diagram in a Corvette service manual. The service manual can be found at your local library. Most Chevrolet dealerships will provide the radio wiring diagram free.