it has something to do with the NBS name brand speaker relay in the fuse box under the hood it has to be turned on for the speakers to work the original radio turned it on via a message sent over the network if I remember right u will need to jump the relay or have it turn on when the radio is on.
I found this, which may help.
I know there is a lead for the radio for it, but there is nothing corresping to it on the harness.
I did find an Infiniti wiring harness which indicates it should go to pin 1 on the C2 connector, which is the black one. I'll have to investigate that also.
"The amp relay is in the Relay/Fuse box located under the hood. The amp relay is the one labeled NBS which stands for Name Brand Speakers.
If you are trying to install an after market radio in a 2001 Chrysler Town and Country, you may notice that no sound comes from the speakers. This is because the single wire that is connected to the factory radio sends a signal to the Bus which tells the relay to turn on - powering the factory amp. I bypassed this by running a wire from the red Acc power wire on the radio to the relay. Connect the wire to pin number 87 on the relay. When standing in front of and facing the van, pin number 87 is the pin, on the NBS relay, which is closest to you and furtherst right"