I bought a noname onboard preamp with an integrated piezo buffer a while ago, prewired but with a missing pot and switch. Fortunately, I found a small pic on the web showing the original state of the preamp, and here comes the mystery: In the pic, the switch is connected to the preamp via 3 wires. On the preamp, they correspond to points labeled P, GND and M. GND is obviously ground, judging by the label and the wiring. I don't know what P and M are, what the switch does and whether it's a 2-way or 3-way switch or whatever. I assumed P and M stood for Piezo and Magnetic, which would mean that the switch is 3-way, toggling between piezo, piezo+magnetic and magnetic. However, common sense and Gibson guitar wiring schematics tell me that there should be a 4th wire carrying back the blended signal from the switch in case of a 3-way switch. I want to hear some opinions from more experienced people before I start experimenting (I'll start as soon as I decide on a piezo solution). Here's the only website I found it on: http://www.artmusicdf.com.br/circuitobaixo.html and here is the pic I'll also post more photos of the actual preamp I have if required.