Brent , this is for a single piezo, but 2 in parallel you just connect both reds together, same with the blacks, in series, you join red of piezo 1 to black of piezo 2 or vice versa---http://handmademusicclubhouse.com/photo/piezo-volume-jack?context=a...
so to verify before soldering, the second piezo follows the same red/black as the first both going to the pot?
Parallel dual piezos: Solder piezo wires same color to same color, then each color to guitar jack or volume control (black is negative, red is positive).
Serial dual piezos: Solder the black wire from one to the red wire from the other, then solder the remaining leads to the guitar jack or volume control.
On the guitar jack, the center is negative, the outer is positive.
Yes Brent, just join them to the pot as in the diagram, as if they were a single piezo
You can also use a capacitor at the jack to tone down the high pitch, although I've never found it necessary to do so if the piezo is mounted well.