LED Brake Light Convertion to Tail / Stop Light

This isn't a new idea and has been mentioned before in these forums. But when I needed it, I couldn't find what I was looking for in one place.

A (very expensive) addition to the Honda top box is the colour matched spoiler. It comes complete with a row of high intensity Red LEDs which are plumbed into the brake light circuit. High level brake lights are now a legal requirement for all new cars in the UK. They are a pretty good idea on the ST1300 too.

However, if you have ever followed another ST1300 in poor daylight, you soon realise how poor the rear lights are. This little modification converts the LED brake lights into a tail/stop light. It requires a few electronic components - 2 diodes (or rectifiers) and a resisitor, some wire and (optional) a couple of electrical connectors.

The idea is to feed the LEDs with two power inputs. One from the brake light circuit, another from the tail light circuit, but at a reduced voltage. The diodes are there to prevent the power from the brake light circuit flowing into the tail light circuit and vice versa.

It took a little experimenting to get a resistor of the right value. The tail light mustn't be too bright, or it won't be possible to tell when the brake light comes on. Too dim, and there is no point in having it !





A split image - left side showing the tail light, right side showing the brake light.



Circuit diagram The 3 wires from the left are tapped into the 3 leads going to the tail stop light.
Green = Earth
Brown = Tail Light
Yellow / Green = Brake light

Please check the colours of the leads to your tail light rather than relying on the ones shown here.

The two wires on the right go to the LED brake light.

The two diodes are 1N5400 - more than big enough for the job
The resistor is 220 ohm, 7 watts. Again, I've gone for overkill.





The photos above shows the components laid out on the circuit diagram. The second photo of the diode shows the orientation - that grey stripe at the end is in the same location as indicated by the black bar on the diagram - in this case pointing to the right.


Note the white 2-pin connector on the right is designed to fit into the connector provided with the Honda spoiler. Check that the colours of the wires match before connecting together.
The green connector on the left is optional. There is nothing to plug it into unless you put the female part in place yourself. The alternative is to hard wire it in place. I prefer to have connectors - it makes it easier to replace the module if necessary. In fact, in the event of failure, I have a simple lead which connects the green connector to the white to reinstate the LED as a standard brake light. And I made two of these modules so that if one fails, the other can be plugged in to replace it.



A shot showing how I wired this up. The size of the resistor in its hard rectangular ceramic case makes a sturdy device to which the diodes can be secured. The diodes were taped to the resistor and the ensemble was then put into a length of 3.5cm wide heat shrink tubing and effectively shrink-wrapped - leaving two wires at one end, 3 wires at the other. This does not show the green earth wire which simply passes from one side to the other. Neither does it show the connectors.

I didn't have the correct colour wire at hand. The orange lead is the one from the +ve tail light circuit (brown on the diagram). The yellow lead is the one from the +ve brake light circuit (yellow / green on the diagram). That dark grey looking lead on the right alongside the yellow is actually a shadow from the flash !

I didn't take a photo of the finished component. Next time I'm delving in the rear cowl, I'll take it out and take a shot to complete the story.


To get at the wiring for the tail stop light, remove the rear mudflap - 4 bolts. The rear light holders can be removed (best to undo both sides. The right lamp holder is connected to the wiring loom, the left is connected to the right. I found that there was more wiring to play with on the right hand bulb holder. Best to remove the bulbs (don't touch with fingers), otherwise you risk breaking them and kneeling on the broken glass. If you decide to cut and crimp on new connectors, make sure you have enough length of wire to operate the crimp pliers. You might need to work closer to the bulb holder than you would prefer.

NB - Make absolutely certain that you have the diodes facing in the correct direction - that grey band must face in the direction of the LED wire. Also make certain that the connector wires are in their correct place.

In the UK, Hitachi connectors can be found at SG Motorsports.
In USA this is one supplier mentioned in a different post http://www.electricalconnection.com/
Diodes and resistors bought over the internet from Maplins (UK)

Good idea and excellent write-up John. Thanks for taking the time to sort out all the required parts and posting photos of the end process.
Regards,
Terry

I like the idea of the strobe brake-lamp, elsewhere written up. LEDs under the lens, 30 flashes in the first second of implementation.

Me_cmc said:

30 flashes in the first second of implementation

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30Hz seems a little fast to be seen as a strobe. Who makes this light?

ST Gui said:

30Hz seems a little fast to be seen as a strobe. Who makes this light?

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Pardon me—I misspoke. Come to think of it, 30 MHz wouldn't even look like a strobe, it would just look solid. At the end of the following video, it says it flashes three times in the first half second. http://youtu.be/7eQbehqomto

Hi John. Thank you for the clear instructions. I'm just about to attempt this. I note you used 220 ohm resistors after experimentation. I just happen to have a 330 ohm resistor lying about. Would this make the tail light too dim? Many thanks.

Nice Job, I did this to my Hondaline box about 5 years back, It's another light from the rear th warn cage drivers!

I wired a double row of led's into the trim piece on my 37 litre GIVI monokey topcase. Seems to me that the 30 ohm resistor provided a striking difference between running lights and brake lights. I used diodes as well. The topbox comes with no lights but the trim piece accepted the led's just as if it had been designed for that purpose. Made a remarkable difference. will post pics when possible.

Thanks John. Appreciate the feedback. Off to maplins as we speak...so to speak.

I found that the voltage drop across the diode actually reduces the intensity of the LED bar when braking. So I came up with a solution with a power MosFET instead of a diode. The brakelight intensity is much better this way.

jfheath said:

Question - in your diagram you have a 330 ohm resistor for the normal tail light. I reckoned that 220 ohm gave me what I wanted - which was something brighter than the normal tail light. If the 330 ohm resisitr was replaced with 220ohms, would the value of your other components remain the same, or would they need to be changed ?

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You should be able to leave those resistor values alone. They are there to bias the FET for operation.

jfheath said:

Another question - I have read (dangerous thing, reading) that installing 'switching' electronics in the brake light circuit can have an effect on the operation of the ABS system on some bikes. I haven't got a clue whether this might apply to the ST1300 ABS system, or whether the MosFET circuit falls into this category but not knowing enough about it made me cautious enough to shy away from that as a solution. Do you know ?

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I have read where inserting some electronics into the brake system (i.e. brake light modulators) can affect the operation of some cruise control circuits like the Audiovox unit that used to be popular around here before they were discontinued. Perhaps you were confusing the two issues? I also have looked over the schematic for the ST1300A and cannot see any reason why the ABS system would be affected by this circuit. There is no connection between the brake light circuits and the ABS computer.

FWIW, I also have been using the combination tail/stop light setup for several years now and I like it. I used the circuit originally described here but also played around with resistor values because I wasn't certain what the original poster had actually used (2 X 330 ohms, in series or parallel???). I ended up using 470 ohms 1W resistor since I had some of those lying around. I was more interested in having a sharper contrast between the two different modes of operation. Does it mean that the light is not as visible in daylight while in tail light mode? Perhaps, but I figure that the BDC aught to be able to see me just fine in the daylight regardless of the tail light operation.

A couple of years ago I added this into the circuit so that the light bar flashes three times first while going into brake mode. I've been pretty pleased with the results although it appears John that this is not an option for you fellas across the pond...

Superdirk said:

I found that the voltage drop across the diode actually reduces the intensity of the LED bar when braking.

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LED's are not voltage sensitive, brightness is controlled by the amperage you drive through it (yes, it is assisted by voltage, but that is not the drive).
So if you are dropping the voltage a bit across the diode then you can ease up on your resistor value to maintain the same amperage across the LED.
You can also use other types of diodes that have less voltage drop.

Ever see someone try to use a variable resistor to dim an LED, not very effective, great for incandescent light bulbs, but not LED's.

jfheath said:

Thanks for that info - its good to have that diagram in the same place.

Question - in your diagram you have a 330 ohm resistor for the normal tail light. I reckoned that 220 ohm gave me what I wanted - which was something brighter than the normal tail light. If the 330 ohm resisitr was replaced with 220ohms, would the value of your other components remain the same, or would they need to be changed ?

Another question - I have read (dangerous thing, reading) that installing 'switching' electronics in the brake light circuit can have an effect on the operation of the ABS system on some bikes. I haven't got a clue whether this might apply to the ST1300 ABS system, or whether the MosFET circuit falls into this category but not knowing enough about it made me cautious enough to shy away from that as a solution. Do you know ?

Click to expand...

Replacing the 330 Ohm for 220 Ohm should be fine, it just defines the brightness in running mode (brakes off). It has no effect on the switching of the circuit.
My aim was to match the original brightness of the taillights and to see a very clear difference between braking and riding, which required 330 Ohm. If you are going for brightness in normal running mode, well, go for it !
Since this circuit is behind the regular brake lights, it is highly unlikely that they could interfere with the working of the ABS system / brakelights. Been working fine for a couple of years now.

Hi guys. Mod done without any dramas. After holding my breath whilst drilling the top box all seemed easy. Really pleased with the results so many thanks to you all.