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Here is the LEGO "LEGO® Power Functions Extension Wire" (8886):

enter image description here

We can see that the left connector can connect to old 9V electric bricks or wires and the right connector can be plugged to the new Power Functions connectors.

The LEGO website gives this description:

Power up your LEGO® Power Functions creations with this 8" extension wire. Make your models bigger, better, and more mechanized than ever before!

  • Allows you to connect your LEGO 9V electric systems to the new Power Functions!
  • Extension Wire is 8" (20cm) long

(emphasis mine)

Does this cable work in both directions?

  • Can it power a new Power Functions motor from an old battery box?
  • Can it power an old motor from a new Power Functions battery box?

Do switches like the old one or new one let you control new and old motors respectively?

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According to Customer reviews on the official website, this cable enable powering motors in both ways between old and new power functions versions:


This cable allows you to power the new 9v motors from the old 9v system or vise versa..

Author: heavyD.


But there is an incompatibility between the old battery boxes and the IR receivers:

This cable also powers new motors from the old battery box, but it cannot power an IR receiver, which requires the new battery box and all 4 wires of the new cable. (This cable only converts the 2 motor-powering wires.)

Author: Technic010.

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I performed my own tests with:


Here are the results: it works in both ways with motors and battery boxes.

Old 9V motor powered by new Power Functions battery box, with the 8886 cable plugged to the motor through the electric plate:

enter image description here

(the cable is out of the photo frame but I guarantee that there's no trick)

New XL motor powered by old 9V battery box:

enter image description here

As you can see, the connectors of the 8886 cable have different colors, the 9V-side is a lighter grey.

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Power functions has four wires, "Electric system 9V" only had two. Two wires carry the motor control lines. The other two wires carry a power supply which is fixed polarity, never speed controlled and is not switched by the IR receiver (though it is switched by the switch on the battery box). The adapter cable connects the two wires of the Electric system 9V to the two motor control lines of the power functions.

Things that will definitely work:

  • Powering any "Electric system 9V" kit from a power functions power source/controller. Some of the Early kit will require use of an Electric plate or an old style cable because it has it's contacts on the bottom.
  • Powering an ordinary power functions motor or a set of power functions lights from an "Electric system 9V" power source/controller.

Things that definitely won't work.

  • Powering a power functions IR receiver from an "Electric system 9V" power source.
  • Powering the power functions servo motor from an "Electric system 9V" source.

Things I can't find enough information on.

  • How the power functions switch behaves. In particular whether it draws it's input power from the fixed-polarity lines (which would make it incompatible with "Electric system 9V" power sources) or from the motor lines (which would make it compatible with "Electric system 9V" power sources).
  • 1
    Actually there IS a way to power IR Receiver/Servo motor from an old 9V power source - daisy-chain them to a new (empty) battery box, switched to the correct position (can't remember which one) - that way the switch in the battery box powers the power supply lines as well. Maico Arts uses that trick to power his servo-motor GBC modules, for example – Joubarc Jan 9 '18 at 8:47
  • mmm, just be careful about polarity.... – Peter Green Jan 9 '18 at 13:06
  • Yes, definitely - I didn't emphasize this enough with "switched to the correct position" – Joubarc Jan 10 '18 at 14:54

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