I have a 1972 Olds Cutlass Supreme with an AM radio (mono) and 8 Track tape player. I am trying to determine which of 2 blue wires is to the rear speaker. (One of these wires is up under the dash so far that I cannot see it) The fader control on the radio has a potentiometer on the back side. I am wondering if this potentiometer can be damaged by playing the radio without the speaker attached. Also where does the wire from the rear speaker run through the car to the dash? I assume it is somewhere under the carpet.

 

Correct

 

Pictures Pictures. Single blue wire to the speaker?

Am I wrong thinking that there is no such thing as a factory mono eight track?

 

The radio is mono and the 8 track is stereo. Only uses one wire for the speakers.

 

The 8 Track connects to the radio via the 3 blade socket (on the back of the radio) and also to the original 3 blade plug in the harness.
There is switching in the 8 Track such that when you insert a tape, the 8 track turns on and removes power to the radio. The switch also disconnects the front dash speaker from the radio and connects it to the 8 Track. The rear speaker is switched as well. It's likely the wiring is buried up in the dash so you don't see those connectors. Which jives with your comment that one blue wire cannot be seen.
The blue wire is for the rear speaker and is under the carpet.
You will not damage the fader (potentiometer) but its not advisable to play the 8 track or radio without the speakers. Delcos did not fare well without a speaker connected. Or a shorted speaker for that matter.
Hope this helps.