I tried answering this 2 days ago but had connection issues. See what kind of readings u get from the speaker- connect a multimeter to the = and -.
What kind of car we talking about? I think u blew the speaker since you are adding power to the stereo signal which is already at say 10-25W. My guess is the voice coil is shot- get new speakers. If the amp detects the short it will shut off automatically. Next time go direct from the amp to the speaker to get a better cleaner sound and make sure u match the speaker with the amp. Buy some speakers which are at least 75% of the amp channel power u use. But not over 100% since u blast your music. please update to see how this goes to help others with the same issue.