I bought this bass several months ago and was unable to find out what the toggle switch does from seller or builder, Hopefully you can help. Here goes. - The bass has Bart p/u and preamp. The pre AMp consists of: Bass, Mid, Treble, Pan, Vol, pull defeat, and the mystery switch. - The pickups are wired directly to the toggle switch. The toggle switch has three positions: 1, 2, and 3. - Positions 1 and 3 sound about the same and make the sound somewhat thin. - Position 2 (mid position) gives a full sound. - The switch is the blue component in the pictures. Hope you can Help.