You need to save the code to your Mach3Mill (or Mach3Turn) folder. Like this:
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ActivateSignal(output4)
Save as Mach3/macros/Mach3Mill/m100.m1s
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DeActivateSignal(output4)
Save as Mach3/macros/Mach3Mill/m101.m1s
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Works good just tested it.
Darek