Laws vary from State to State and you didn't mention if the gun was loaded or not. Definitely check with a lawyer familiar with the subject in your state. I was curious as to why your son would have even mentioned the gun during a routine traffic stop. If the gun was locked in the glove box, a police officer would have needed probable cause to search the automobile, especially to open a locked glove box. Had he never mentioned the gun, it never would have been discovered. While I'm not advocating doing anything illegal in your state, he should have known the law. He wasn't however under an obligation to incriminate himself.