This is a stereo jack with switch contacts.

Wiring instructions for guitars using RMC piezo/13pin:

Pin 1 - connect to ground/sheild
Pin 2 - connect to wire # 15 (green) from the 13pin polydrive cable
Pin 4 (TIP) - connect to magnetic guitar signal, output of the volume pot (center leg)
Pin 8 goes to RING - connect to piezo guitar signal, output of the piezo volume pot (center leg)