1988 Grand Prix Radio does not work

My 1988 Grand Prix SE radio does not work. The clock always shows 1:00 and you can push a few of the buttons and they seem to show up do not work...ie. SET. This shows up but does not work. I am not able to hear music. I am able to power the radio on and off but it sticks on volume 5 and 98.1 and I am not able to change. I purchased a used radio...guaranteed not DOA. I plugged this radio and cassette player into the car. It is stuck on volume 5. I am able to push the buttons to change stations and they do work but no music. I am completely lost as to what why I am not able to hear music...adjust the volume...not set the clock...it is stuck on 1:00 as well. Can someone give me a heads up as to what may be wrong with this car? Thanks!!!

bad raidio or wrong wireing harnes.

I have tried three different radios and they all worked when the came out of the cars. It cannot be a bad radio. Every radio I plug into the harness does the same thing. As far as wiring I am not sure how it can be bad wiring since the radio just stopped working one day. Something had to go bad. I just have no idea where to check or how to check!

fuse? thats all i can think of.

Use a DVOM (digital volt Ohm meter) to check for continuity? Maybe the wires have a bad ground.

Thanks for all the information...I have finally found someone who was able to help out. This year of Grand Prix had a third piece...a tuner amplifier. The controls are just that...a control box. But no one can tell me where it is located in the dash for sure. I am going to have to just start tearing the dash out I guess.