Explain how this dual foot switch circuit works please

[Randall]

http://www.thetubestore.com/lib/thet...-Schematic.pdf

This has always perplexed me. How does this circuit achieve two separate switching functions with mono or two conductor cable? I sort of get it, but can't get past the reversed bias diode on the FX side.

[Jazz P Bass]

Because of the LED & the zener diode, you end up with 2 separate & distinct switching voltages.

From there it is explained in the switching voltage chart.