There was probably a factory amplifier that needs to be bypassed or turned on. Only Chrysler radios all put out speaker level audio whether the vehicle has an amp or not. Their amps don't increase volume or power. They are only for tone conditioning for the shape of the vehicle. On GM and Ford products, radios that use an amp have to be used with an amp, and those that don't use an amp can not be used with an amp.
If your new radio has RCA jacks, those are low-level audio and can be wired to a factory Ford or GM amp. If you don't have an amp or want to remove it, your new radio will also have the standard speaker-level wires.
All factory amps have 12 volts there all the time. There is a separate wire that needs 12 volts to tell it when to turn on. Your aftermarket radio will also have the wire to turn on remote things. It's usually a yellow wire labeled "power antenna", but it can be used for an amp too.
Be aware that by the mid '80s all car radios had two wires going to each speaker. Same is true for all aftermarket radios. None of the speaker wires can be grounded like they were years before that.
Thursday, June 16th, 2016 AT 7:39 PM