Tutorial Written By Fellow Member Jackpilot
here is a small gizmo that can tell you when a circuit is open or closed.
Actually, the best is a $20 multimeter but let's start with that.
You need a battery and a bulb , any battery, any bulb as long as the voltage of the battery is not higher than the voltage of the bulb, polarity is not an issue.
Alligator clips on A and B are a good idea.
Test your contacts with A on one B on the other, if the bulb lights up circuit is closed, and vice versa.