So he connected the speaker directly to the connector that plugs into the radio and there was no sound?
That would seem to suggest the radio itself is faulty, but you said you had the same problem with the original radio too.
Yes...so now he's plugged the stereo directly into a different car battery. Everything works perfect. The external speaker and the car speaker when he tries it.
So is it something with the power since it seems to work fine when hooked up to a different power source.
Update: Happy Days. I took it to the audio place and he did a simple test and we were looking in the wrong place. Turns out both rear speakers had a short so he just disconnected them and we're good to go.
He didn't charge me and if my son wants to install new rear speakers he can but I don't think he's too fussed.