Speaker Power Detector
One more thing. Right now, if you have an unusual amplifier or if you wire your amp incorrectly to the power detector project, you could short out your amp’s power outputs. Before building the project, use a continuity tester or ohmmeter to make sure your amp’s black (ground) speaker connections are tied directly together (< 1Ω resistance) inside the amp, and make sure you wire the amp to the power detector correctly.
   Speaker Power Detector
For more detail Speaker Power Detector website
www.neufeld.newton.ks.us