Here is what I learned when I took my aftermarket radio out and went to a stock configuration
I believe it was possible to have 1,2,3, or 5 speakers in the car from the factory.
1 = Single front
2 = Single font, single rear (AM with a rear speaker knob)
3 = 3 front speakers (AM/FM no rear speaker knob)
5 = 3 front, 2 rear (AM/FM with a rear speaker knob).
Both the 3 and 5 speaker versions were stereo and used a cross over box. The cross over box is the same for all configurations for all years,
The 2 and 5 speaker versions used a rear speaker fader knob. However, the 2 speaker fader and the 5 speaker fader are different (different number of wires etc). The 5 speaker knob will have a short set of wires and go to a 6 pin connector. The 2 speaker fader does not have 6 connections and the connector for mine was located behind the driver's kick panel.
The 4 wire harness to the rear is for two speakers, 2 wires to the left, 2 to the right. I can't remember which is which but you should be able to figure it out with simple trial and error using the L/R balance.
I ended up wiring my car as a 5 speaker, even through I have only 1 in the front. I just left the L/R front connections empty.
Here are the best diagrams I found:
I got them from this thread over on moparts:
http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=5415364&page=0&fpart=1&vc=1You need to log in to see the pictures but they have images of a number of the components involved.