This is a Passive A/B/Y switch box with input grounding (for the input not in use). There are some examples of how to use this box below. The circuit is passive except for the LED indicators to indicate which “channel” is active. The two channels are interchangeable as input or output channels as illustrated in the examples below. This project is more complicated than some due to the input grounding. There are some simpler version schematics in the section below these project files, in case you want to chose a simpler version.

Description from General Guitar Gadgets.