Step 1: What's needed.
1 guitar amp.
1 - female phono plug
1 - Good piezo buzzer
1 guitar phono plug cable to go from guitar to amp.
double stick pads
Drill and bit.
Step 2: Title this StepA palce for the phoneo plug.
Step 3: Soldering
Solder wires from piezo speaker to phono plug
Cover connection with electrical tape,
Step 4: Putting it together.
Put soldered units in guitar but do not let go.
Arrange the the phone plug so it fits through te hole you drilled.
Screw on nut for phono plug.
Gently lay down piezo speaker.
Put double stick layer on support near the bridge.
Place piezo speaker on double stick layers.
Set aside to let the stickum dry for a bit.
Note: Removed original picture for updated picture.