Does anyone know what the wires do?

If the Power Functions train motors are simple DC only 2 wires would be needed or is it more complex than that?

1 Answer 1


The LEGO Power Functions connectors have 4 standard designations regardless of the usage:

  • 9V power
  • "0V" Ground
  • C1 "control 1"
  • C2 "control 2"

It seems for motors that the 9V and Ground are unused. The C1 and C2 are used in combination to pick the motor direction. If C1 is providing power and C2 is providing ground then the motor goes forward. If C2 is providing power and C1 is ground then it goes backwards.

power function motor diagram

The dashed lines are unused at that stage in the flow.

  • 1
    To drive two motors in opposite directions at the same time from one output of the remote unit all I need to do is to reverse C1 and C2 on one of the connectors?
    – Quorneng
    Commented Dec 11, 2017 at 15:57
  • That sounds reasonable.
    – chicks
    Commented Dec 11, 2017 at 16:04
  • 1
    If you're using the standard battery box, and no remote, that is the difference between the two on switch positions Commented Dec 19, 2017 at 9:21
  • It's strange that they chose to do the reversal by adding 2 more lines rather than just reversing the polarity of the power. It means there has to be logic in the motors as well as any switches you add to the chain.
    – John Stock
    Commented Dec 5, 2023 at 22:06

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