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I have a number of old technic motors and battery boxes I would like to use however the wires have disintegrated in storage to the point that the metal conductors touch and short out.

Does anybody know the best wire to replace them with? I'm thinking it probably needs to be flexible multicore but I'm not sure of the required current capacity or AWG?

  • Great question! Welcome to Bricks.SE! – jncraton Jul 23 '18 at 13:37
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MindS1 is correct that in terms of electrical properties you don't need to be terribly picky. As you noted you will want multicore wire to allow for flexibility and prevent breakage.

I'd also add that the standard 9V battery boxes are current limited, so in practice you can get away with 22 AWG or even 24 AWG wire. I'd encourage you to try out the wire in advance to make sure it meets your power requirements. A pair of buggy motors is very different than a few lights or a train motor.

It is possible, though more difficult, to replace the entire wire rather than splicing out and replacing the bad bits. This is covered in detail on Instructables. Here's the gist:

  1. Carefully remove the back plate from the connector using two flat blade screwdrivers to release the clips:

opened connector

  1. If you are using a compatible wire size, you can simply slide the wire into the metal clips exactly as the original wire was attached. Otherwise, you can solder it in place:

soldered wires

  1. Pop the back plate back on being careful to route the wires and tabs appropriately.

If you are working with the longer wires, and the break is near the end, you can simply remove the wire, cut off the bad end, and reconnect the remainder of the original wire. Your wire will be a few cm shorter, but that isn't a big deal for many applications.

  • Thank you for the pictures, that's incredibly helpful. In the second picture, have you routed the new wire over the black plastic tab that I assume is for cable strain relief, or have you removed the tab? I can't quite tell from the photo and I'm struggling to get my replacement wire over the tab on mine as I think the insulation on my new wire is thicker. – Ralph Jul 24 '18 at 9:20
  • I didn't take those photos, so I can't say for sure. I wouldn't think it would hurt to cut that tab down if your wire is thicker. – jncraton Jul 24 '18 at 20:24
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You don't really need to worry about the wire gauge for Lego parts. This source indicates that only the beefiest lego motors breach 1A, and even then, only while completely stalled. Most of those motors even have thermal protection systems built-in to prevent damage in the stalled case. So anything around gauge 20 or lower would do the trick.

Make sure to get a stranded core instead of a solid core so it will be flexible.

After you trim out the old damaged wire, slip on some cheap heat-shrink tubing over the remaining part before you twist/solder on the new wire. The heat-shrink tubing will reinforce and protect the new connections you made.

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