In this adrenaline-filled safari into appliance repair excellence, Samurai Appliance Repair Man shows you how reverse-polarized wall outlets can pose unexpected dangers to you on a service call. Don't be a victim! Watch this video, save your own life, and learn a few appliance repair tricks and tips along the way. Better yet, enroll in the Samurai Tech Academy and learn all about basic electricity, series and parallel circuits, motors, troubleshooting, reading schematics, and much, much more!
Just to point out a couple of things shown in the video.
First, the relay on the control board in this case is switching Neutral instead of Line, as it was designed to do. This is actually easier on the relay contacts since there won't be any arcing like you'd have if it were switching Line.
Second, although the gas valve has Line voltage standing at the terminals because of the reverse polarized wall outlet, this does not pose a danger to the appliance... just to the unaware appliance tech!