This was answered in another post, but here's a copy and paste version for our friends searching for the answer to this problem:
The amps get 12 volts from a relay that was turned on by a "Switched 12 volt" terminal in the black connector. If you removed a cd / cassette combo radio, these are made by Mitsubishi and are very high quality. The amplified speakers are too. I just bought a dozen from the junkyard.
All Chrysler radios put out speaker level output to run speakers directly without the need for an amplifier. Eliminates the confusion found in GM and Ford systems. Rather than having dozens of different radios, like GM, Chrysler uses the speakers to modify tone response to the shape of the vehicle, not to affect volume.
Any high quality aftermarket radio will have a switched 12 volt wire that is used for a power antenna or remote amp. That wire is often blue. It must be tied to the wire at the end of the black connector, furthest away from the keyway. It could be dark green with a red stripe, but the colors might change from year to year.
If your radio doesn't have a switched 12 volt wire, connect the relay wire from the black connector to the 12 volt power wire from the ignition switch. The car's wire will be red with a white stripe and was the second from the keyway end of the gray plug. This wire turns off with the ignition switch. Don't use the pink wire from the car's harness; that stays on all the time for station and clock memory. Using this wire will run the battery down overnight.
If you still don't have sound after connecting the amp relay wire, be sure you're using the speaker wires of the new radio, not the RCA outputs, if you have them, because those are very low level output and won't run speakers directly. I don't think that's your problem, however, since a different speaker worked.
You should also be aware that the original radio in this system did not put out much bass; that was made up in the speaker amps. Using a non-Infinity radio can result in a lot of bass so don't be surprised if you have to turn the bass all the way down to make it sound decent.
Tuesday, March 24th, 2009 AT 4:27 PM