Looking at the diagram below you will see that there are 5 connections points.
Input (1,2) - connect to the Printrbot fan connector.
NO (3), C (4) and NC (5) or Normally Open, Common and Normally Closed.
In this case you want to use the Common and NO (Normally Open) connection.
When the Printrbot PC board tells the fan to turn on, the electromagnet
will activate and cause the switch to move from NC to NO. This completes the path
between the power source and the Load ( Fan or ? ).
If you have never done this before I would suggest you find a local person
to over watch what you are doing. I would not want you to end up with a
printer that is not working because you were trying to improve it.
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Printrbot Simple Makers Kit (1405) modified.
It's all in the details!