This probably won't help you much, and I apologize in advance for posting this.
I had a Ford radio with a CD player and I added an aux-in port to it by tying a phono-jack into the CD-player audio out traces.
Then, what you had to do it use Audacity to record about 75 minutes of 'dead air' into a .wav file, and burn that as an audio track to a CD.
To listen to the aux-in, just play the 'dead air' CD, and the aux-in audio at the same time (hint: all you would hear is the aux-in).
I totaled the 2000 Windstar shortly thereafter and got a modern non-motherly vehicle with BT audio, SYNC, SiriusXM, Pandora, USB, and... aux-in.