Guide to making custom length Power Functions cables / adapters

[BatteryPoweredBricks]

TLDR video at the bottom of the post

In my builds / layouts there is one common theme, needing longer Power Functions cables.  At least with this system Lego provided extension cables, but even those are fairly short and getting more and more expensive.  Third party extensions are available but still not long enough for me, and they use embarrassingly small gauge for the wire.  Sure you can daisy chain them together but each connection and the length of small gauge wire will introduce enough resistance to cause issues (ask me how I know).  I was very happy to find the 24gauge BNTechGo wire I had been using for making 9v cables works great with PF connectors.  It seems a bit oversized at first but it's good to go as high on the gauge as you can so you can make longer cables without issue.  The extension cables are very easy to make, just be sure to reverse the connectors so the 9v supply wires are the correct polarity (ex. studs up on one end of the wire and studs down on the other).  Links to the products used are in the description of the video, this way I only have one thing to edit if anything changes in the future. 

 

I'm also quite fond of making adapters to be able to power IR receivers and PF servo motors from a 9v source such as an RCX or train speed regulator.  This can be done with the official Lego 9v adapter and an empty PF battery box to short the control wires with the 9v supply wires, but making your own adapter cable is a much more elegant solution.  I have a standard that I use to make sure I don't reverse the polarity of the 9v supply.  This is what the connector looks like internally.

 

 

And because I just couldn't help myself I went ahead and made another wire tester.  The RCX grabs ground from the sensor port and send 9 volts to each output one at a time.  These 4 wires are put into a PF connector and then I have another connector that breaks out to three 9v lamps.  At least in theory this should show if there is any issue.  If any pin is not getting continuity one or more lights will not light up.  If there is a short multiple lights may light up at a time or the first lamp will fail to light.  pictured next to my 9v wire tester.

 

 

UPDATE: I've uploaded a new tutorial which fixes a few mistakes in this video and has a lot more information.  I should have mentioned the above jumper cable would create a short when used in reverse (powering a 9v motor from a PF source). 

 

 

(old video) And of course here is the video I made, which goes into a bit more detail and I can actually show you how I make these cables and how I use them.

 

 

Edited November 7, 2023 by BatteryPoweredBricks

[dr_spock]

I have some 35 years-old ribbon cables and used that.  Funny, it is still good compared to my LEGO 9V cables.

I had to adjust the spacing of the individual wires.  I wonder if old flat 4 conductor telephone cables would work too.

 

[BatteryPoweredBricks]

11 hours ago, dr_spock said:

I have some 35 years-old ribbon cables and used that.  Funny, it is still good compared to my LEGO 9V cables.

I had to adjust the spacing of the individual wires.  I wonder if old flat 4 conductor telephone cables would work too.

 

I'm sure there are many wire alternatives that would work.  For me I'm particular about aesthetics and I want a decent gauge wire for long runs.  I've had issues with long runs not getting enough power for PF servos using cheap extensions I bought online (demonstrated in the video).

[Fyredog]

How Many times I could have just done this instead of figuring out how to hide the terminals in my Builds!