CIRCUIT CUE - A must for any Serious Mobile DJ
CIRCUIT CUE + KLEIN Tester are two devices you need for testing AC electrical circuits.

Test the receptacle outlet for power and detect wiring problems before you connect..
Instructions:
1. Plug the KLEIN tester into each receptacle being tested to vertify the circuit is on and wired correctly.  
2. Then plug the Circuit Cue into a receptacle outlet.
3. With an IEC cable plugged into the bottom of the Circuit Cue, use an extension cord to access an ACreceptacle away from the original receptacle plug that the circuit cue is plugged into.
Note: When the light is ON  you have two separate circuits/breakers.

Edited video from May 3 posting:

Note Never trust anyone's cables but your own! : Complete DJ Barr video link

Receptacle Tester

How and why to use:

Great Video understanding neutral and ground relationships and why a tester is good to have.

How many outlets on a circuit breaker?