I'm putting together a 2x12 with two different speakers. I'd like to wire it with three jacks... jack 1 = speaker 1, jack 2 = speaker 2, jack 3 = both speakers, ideally in parallel. Some weak googling turned up a few pre-made items that seem to do something similar, but not this exact thing. Can anyone point me to a wiring diagram or a pre-made harness for this? Thank you.