SeGiven that it’s the Holidays, there’s a good chance that you are putting up some lights. Which means you need extension cords. If you are running LED lights, you want an small, flexible, extension cord that can carry a small amount of power – 100 watts or so.

You cannot buy such an extension cord, because somebody would plug a hair dryer into it, melt it down, and catch their house on fire. Which would be bad.

There is a way around this. If you put a fuse in the extension cord to limit the current, you could use smaller/thinner/cheaper wire. In fact, whenever you plug one light string into another, you’re using the first string as an extension cord. If you have any old light strings lying around, it’s easy to convert them to extension cords.

Step 1: Gather your materials

You will need one incandescent light string. You can probably find one that isn’t working for free.

and you need a few tools and materials:

Clockwise from the left, there is a wire crimper, crimp-on connectors, a wire stripper, diagonal cutters (aka “wire cutters”), and a hot glue gun.

Step 2: Getting rid of the lights

Light strings are built in the following manner:

• There are two wires that go from one end to the other (so you can plug in the next string).
• There is one wire that has all the lights on it.

At the start and end of the string, there are special light sockets that have 3 wires going to them. If you have a double circuit (100 light) string, you will find the same sockets in the middle.

Start with the second light (*not* the one with three wires going to it, and cut the wire next to the socket:

Do this for every socket that has two wire going into it. Once you have done this, remove the lights from the string. If the string is loosely twisted, you can just pull it out, but if it’s a tight twist, you may need to unwind it first. When you are done, you’ll have a nice pile of lights and very short pieces of wire:

Not sure what to do with all of these. Any ideas?

Step 3: Getting rid of the 3-wire sockets at the end

Now that we’ve gotten rid of all the bulbs, we need to fix the ends. First, we cut off the 3-wire socket:

There was a wire from this light to the other lights that I already cut off. These two wires are connected inside the socket, so we merely need to remove the socket and connect the wires together. I did one version where I just filled the socket with hot glue; it works okay but the socket can still catch on things and looks kindof weird.

Step 4: Connect the wires together

First, strip about 3/8” of insulation off of the wires:

After you strip the wire, twist the stripped ends tightly. I like to bend the stripped wire over so that it is half the length but twice the thickness so it fits in the crimp-on connector better.

The connector is then crimped on:

Do the same at the other end, and the connection is completed:

 

If you don’t want to use crimp-on connectors, you could solder the wires together and use heat-shrink tubing to insulate. If you take this route, make sure that you know how to do a very good solder joint, and I would probably go with two layers of heat-shrink tubing.

Step 5: Insulate and waterproof

Plug in the hot glue gun and let it heat up.

Hot Glue Gun Safety Hot glue is – not surprisingly – very hot. It is also extremely sticky, so if you get any of it on your hands, it just sits there and burns. Try not to do this, but if it does happen, spread out the glue across as much skin as quickly as possible. This will spread it out and cool it down quickly.

Bend the wire to one side, squirt some glue in, and then bend the wire back and squirt the wire in from the other side. Allow it to cool off, and then do the other end of the connector.

Another option is to use silicone. This is a better solution – the silicone is flexible and will fill gaps better – but it takes a bit of finesse to get it to fill all the gaps and you have to wait for it to cure, so I use hot glue instead.

Once you have end done, do the other one exactly the same way.

Step 6: Do the center portion

If the set you are converting has two strands, there are two 3-wire sockets in the middle:

Fixing this is simple; you just need to cut off both of the 3-wire sockets, and then connect the two wires together. If you want the extension cord to be shorter, you can cut the wires to whatever length.

All that is left is to connect the sections of wire together. You can cut them the same length, but it’s a little nicer if you offset things a bit:

The closer wire is about 1 1/4” shorter than the long one. Cut both wires like this, and then join them together:

Note how they are nicely offset.

Step 7: Enjoy

You may now enjoy your extension cord. Total cost was about $0.50 for the connectors (they’re cheaper in bulk), and a few cents for the hot glue. The plug has a couple of 2 amp fuses built into it, so it is safe to use; just don’t use it with too big of a load or you will blow the fuses.