Hi,
It depends on the amount of damage. You need to take your car to a car electrician and have it checked. If only the AM/FM receiver is damaged then you only have to replace that. If there has been a short circuit then you need to replace all the wirings, the AM/FM receiver, the circuits connected to your AM/FM receiver, you might also need to change your speakers. I had the same problem with my 2003 accord and the electrician told me that my car had a shock circuit so i had to replace the whole AM/FM system, all the wirings,all the speakers and the circuits. By the looks of it I think that your car had a short circuit, but go to a car electrician and have it checked before you do anything.