I have a Shimano DH-3N31-NT hub dynamo with following type of connector:

Shimano Dynamo Connector

Yesterday, diodes in the bridge rectifier of my front LED light exploded. While I was disassembling the light, I noticed that the wires inside of the connector were more than a bit patinated after some 7 months of use.

I'm wondering, what should I do to weatherproof the wires? The dynamo manual, as far as I can see, doesn't mention any weatherproofing steps.

  • 1
    Smear everything with dielectric grease (available from an auto parts store, since it's used on the high voltage components of auto ignitions). Sep 19, 2016 at 1:27
  • 1
    You don't need to care about the patina on the wire in general, only on the bits that are actually in contact with the plug/dynamo. I find that periodically removing and re-inserting the plug is enough. Well, I used to before I got sick of that plug and replaced with with automotive style spade terminals and sockets, with beefier wires. That meant not having to re-do the plug connection every year/5Mm.
    – Móż
    Sep 19, 2016 at 4:49

3 Answers 3


There are a few options:

  • Electric tape (there variants for more waterproof than others)
  • Heat shrink
  • Liquid Electric Tape

I'd probably just wrap the thing in electric tape and call it a day though. If I continued to have problems, I'd go for liquid electric tape, then heat shrink+electric tape. Or, if you can't find liquid electric tape, clear nailpolish might work okay.

  • I was actually thinking of first trying out the nail-polish, since it seems to be among the cheapest available options!
    – AndrejaKo
    Sep 19, 2016 at 16:39
  • 1
    I wouldn't use nail polish. It tends to become brittle and craze easily. Also a bear to take off if any of the nearby are sensitive to acetone.
    – RoboKaren
    Sep 19, 2016 at 17:20

I use ShoeGoo or Sugru (you can Google both brand names) for waterproofing connectors.

The advantage of both is that they are flexible and waterproof, but also relatively easy to remove in the field without any gooey residue (which tape tends to leave). I also find it hard to use shrinkwrap to waterproof connections where the diameter of the two parts is more than 1:2 in ratio, because of the limitations of the shrinkwrap shrinkage. Nail polish becomes very brittle very quickly.

For the dyno connector, I'd use ShoeGoo. Assemble the connector. Put just a very small (lentil pea) size on your fingertip and rub it in like caulking compound on the outside of all mating surfaces. You want to get into all the cracks but you don't want to apply too much and weld things together. . This ensures that you'll be able to still take it apart in the field.

The one exception is where the wires enter the connector body. I might put some ShoeGoo on the outside of the wire before sliding it fully into the connector to ensure that it's well sealed.

As Daniel Hicks has mentioned, some dielectric grease on the bare wires will help. You can get a tiny squeeze tube at the checkout counter of the auto parts store for under $2.


A short-circuit or bad connection in the connector should not cause the LED lamp to break. It probably broke for some other reason. But you'll probably want to deal with the corrosion anyway, as it is easier to do so now before it gets too bad.

First off you'll want to clean off the corrosion that has already happened. A mild acid is a good option, you can read more in this question.

As for sealing, my recommendations would be:

1) Plain old grease (vaseline, silicone spray or even chain lube if you have nothing else). The metal parts will push it aside and make a connection, but it will stay elsewhere to keep water from getting into the area. There are also special greases for electrical connections, which probably work even better.

2) Self-vulcanizing rubber tape. Wrap it around the connector, and it will vulcanize into a seamless tube that stays in place better than normal tape.

  • 2
    Petroleum-based lubricants should not be placed on the plastic components, as they will tend to cause deterioration. Silicone grease is ideal. Sep 19, 2016 at 11:51
  • @jpa Yeah, I'm aware that the bad contacts had nothing to do with the lamp blowing up. It's just that I'm still preparing the lamp question.
    – AndrejaKo
    Sep 19, 2016 at 16:39

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