I am installing a new head unit on my DD 96 Mustang Convertible. It had an older a/m head unit in there so I took it out. I was able to get an adapter for all of the wires except the speaker wires. Now I have the speaker wires to splice in.

I hooked the new stereo up to an external speaker (from my room, not car speaker) and it plays out of that speaker. Then I try to hook it into the correct wires in the car speakers and I get nothing.

I took the old head unit and plug them into the external speaker and it plays sound. I then tried to put that one into the car and spliced it into car speaker wires and it played fine through all the speakers.

Now, if my new stereo can play through the external speaker (not car speaker), then why won't it play through the car speaker?? The car speakers work because the old stereo plays through them no problem.