Retro Bike Taillight Upgrade - Incandescent to LED Conversion (With Magnetic Switch)




Introduction: Retro Bike Taillight Upgrade - Incandescent to LED Conversion (With Magnetic Switch)

I love my retro bikes. I've had about 6 of them over the years and despite their quirks (and sometimes dangers) you learn to love these beautiful steeds.

But you know what REALLY annoys me? My Incandescent dynamo taillights and the amount of tiny little bulbs I've been through over the years! If there's one thing that everyone here on Instructables knows "If it can be made better with an LED, then what the HELL are you waiting for?"

This instructable was created for the 2013 bike competition, It basically substitutes the dynamo system with a closed unit LED system that is triggered using a magnetic switch so to completely maintain the original look, integrity and beauty of the taillight while providing the convenience of a long-life lithium-LED set-up.

I had been thinking about doing the conversion for a few months but the competition gave me the kick in the butt I needed, so here it is!

Strap in Retrophiles, your 1960 stylings are about to meet 21st century reliability!

Step 1: To Begin

This is a fairly simple procedure and anyone who knows simple electronics and bike bits will be right at home with this conversion.

Parts & Tools You'll Need
  • Your original bike taillight
  • 1 cheap LED bike light - One of the small ones, preferably red with a flashing function.
  • 1 small Reed Switch - A type of magnetic switch, I salvaged one from an old cycle computer sensor, but any electronics store will have one.
  • A small Neodymium Magnet.
  • Some thin insulated wire - Again I salvaged some from the cycle computer, you don't need much, 30cm or so.
  • Some decent Electrical or Gaffer Tape.
  • A Soldering Iron, Solder and a Solder Sucker (If that's the way you roll).
  • Willingness to part with tradition.

Find a comfortable place to work with your bike close at hand, Let's get started.

Step 2: Out With the Bulb...

If your taillight is anything like most of my lights disassembly will be straight forward. Look for any screws and undo them. On my model the red plastic cover is easily removed by pulling it forward and up after removing a screw, exposing the bulb. You may need to squeeze the sides in order to release any plastic catches on other models but it shouldn't be too difficult.

Once the plastic cover is off, unscrew and remove the light bulb from within, if you want you can keep it to show your kids, one day. 

As you can see there's STACKS of room inside these things. Keep in mind the general shape of your unit as we are going to have to eventually fit all our components inside, snuggly.

You can leave your bike alone now. Grab your LED stuff and crank up that soldering iron (Provided you know how to use one, careful now)

Step 3: ... and in With the New.

Here's a 2 quid light I bought from Tesco a while ago (Ok, it was a pair for 4 Quid). The silicone snapped but the light is still going strong so we're going to take the guts out of this light and modify it for our needs.

Start by removing the covering, on this particular light it's silicone and is easily removed with some wrangling, some similar lights that have a plastic outer shel and an elastic mount can be disassembled with a small screwdriver.

Step 4: Salvage.

Once you've removed the cover continue by removing the main PCB (printed circuite board) and the batteries, these are the only parts we need.

Step 5: Desoldering the PCB

Now we're going to want to remove the LEDs/LED assembly, the battery contact points and switch contact points then replace them all with our own customisations.

Start by noting where everything is situated, the orientation of the LEDs and the battery orientation.

Start to remove the LED assembly, this is the most difficult part as you may need to use a solder sucker to clear the PCB of all solder before the LEDs will budge, take it slowly and don't leave the soldering iron on the PCB for too long as you may dammage the board.

The existing momentary switch may have some tape covering it, you want to remove both the tape and the small piece of springy metal that forms the momentary switch so the terminals can be soldered to.

Step 6: Wiring

We about to solder the wires to the main PCB in order to fit the electronics to our light casing. Have another look at the casing and get an idea for roughly the length of it, we want to add enough wire to fit the casing correctly, see the diagram attached (Pink = Wires). Preferably the battery will sit flush against the back of the casing, the PCB sits over that and the reed switch to the side or any convenient place at the edge of the casing.

Solder the reed switch and the LED assembly to their dedicated wires.

Step 7: Add the Battery

The moment of truth, complete the circuit by creating an enclosure for the two 3v batteries using a single piece of doubled over gaffer or electrical tape. As this will be the only part you'll have to tamper with in future (when replacing the batteries), keep the wires straight so that the batteries can be yanked off reasonably easily.

Before sealing the battery assembly hold the wires on the correct battery terminals then touch your Neodymium magnet to the reed switch briefly and check the circuit works. If not; Double check you got the polarity of the batteries right, if it still doesn't work check your LEDs are wired correctly and failing that troubleshoot - check over your soldering work.

If she lights up, seal the batteris and the PCB snugly and neatly in gaffer or electrical tape

Step 8: Rough Fit

Now head back to your bike and roughly place the entire assembly in the casing by inserting the battery first and placing the PCB on top with the LEDs in the direction of the old bulb mount.

What you want to do is fold the wires so they poke into the bulb mount cavity, holding the LED assembly in place.

When you've shaped the wire satisfactorily use the old globe as a guide and wrap the wires to make a plug for the globe mount.

Step 9:

Return the entire assembly to the casing, putting the newly fashioned plug in the globe mount as well as fitting the rest of the components. You want the reed switch to sit as close to the edge as possible so that it can interact with the neodymium magnet's field without hindrance. Once you're satisfied that everything is fitting and nothing is getting caught when the red plastic cover is replaced close the casing and fasten any required screws.

And that's it, grab your magnet and test it out but swiping it over the area where you placed the reed switch.

Step 10: Plans...

Where you place your magnet on your bike frame is up to you. I've had my own sitting on my back fender so it looks like a rivit sitting just above the light, I've also stuck one to my removable front headlight as well. Basically you want to have a backup stuck somewhere on your bike incase of disappearance due to overzealous curb jumping, sticky fingers or extreme winds ;)

I'd love to develop a solar rechargeable version of this type of sealed light for my more modern bikes as a theft proof device, if anyone has any ideas on improvement I would love to hear them!

Thanks for checking out my instructable, Enjoy and happy converting!


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    11 Discussions


    3 years ago

    Hi Doody, thanks for the instructable, this looks like just what I need and I've got a very similar component (ULO 230-90). What I can't figure out is how the bulb is powered! There's a cable coming out the other side which disappears under the rim of the fender. How is yours powered?


    Reply 3 years ago

    Hey Fetimo, great to get some action in this instructable! So this is basically a hijacked led vike light powered by the original coin cell (you can use a few in parallel fore more juice) the bulk only made it into the photos to illustrate how to utilise the space it formerly ooccupied. The old incandescent globes (however charming) are nowhere near as bright or efficient as leds. Not sure I understand which component you've got the, thinking maybe a reed switch?
    So just use the circuitry/battery of the commandeered bike light.

    You could go with an incandecent bulb but you're going to need to build the curcuit and 12v power supply to drive it, which would be epic but quite heavy!! One idea I did have was to swap the battery elements for a solar or usb rechargeable one, alas this bike was stolen and I never took on the challenge!

    All the best and happy making!!


    Reply 3 years ago

    Correction * batteries in series.


    7 years ago on Step 10

    Super instructable. Hacking this light fixture to upgrade is great. Your pictures captured the progression very well. DId the original led fixture have a 'clicky' switch? Do I understand correctly then, that the reed switch and magnet replaced the clicky?


    Reply 7 years ago on Introduction

    Hey Bobcat! The reed switch does indeed replace the original 'clicky' switch, or be it simply a circular springy piece of metal that makes contact when pressed down (You can see this component really clearly in figure 5).

    The momentary switch (on when held down) just tells the circuit to 'move' to the next function (On, Flash or Off) when contact is made, hence when the reed switch is closed/activated buy the magnet the same function is performed.

    Saying this, you could replace the reed switch with any momentary switch, ie drill a hole and install one on the top etc, but the 'non-invasive' option was what I was going for here. Thanks for the feedback, Happy building! D


    Reply 7 years ago on Introduction

    Thanks Rimar, Appreciate your encouragement, your track record is an extremely motivating body of work. After many years of treating Instructables as the online bible of think-tank brilliance I'm excited to finally pen a few gospels of my own ;)


    Reply 7 years ago on Introduction

    Thanks Audrey! No worries, It's definitely inspired me to get more of my crazy projects on here! :)