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Connecting LED turn signals on your motorcycle

LED technology opens up a whole new world of vehicle design opportunities. Turn signals are an excellent example, and the good news is that retrofitting LED turn signals is a piece of cake for DIY mechanics.

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Perfect for motorcycles: Light Emitting Diodes

Low power consumption takes a load off the electrical system, small-diameter cables reduce cost and save weight, the powerful light output allows tiny dimensions and imaginative designs, and long LED life saves you the bother of frequent replacement. Especially for motorbikes, a small housing really is a bonus. So it's hardly surprising that nowadays many motorcycle riders choose to convert to smart LEDs when an original turn signal needs replacing, if not before.

Basically, any bike with a 12 V DC electrical system can be fitted with LED turn signals. However, you do need a basic knowledge of vehicle electrics to do it yourself. If you are not confident in this area or you have a motorcycle with complex electronics (e.g. a BMW with CAN bus or a motorbike with start-up system check), you should leave the fitting to a motorcycle workshop. If your motorcycle is still under warranty, you should first check with your authorised dealer if conversion would affect it.

Technical requirements for LED turn signals

LEDs have a substantially lower wattage (power consumption) than conventional incandescent bulbs. You can easily tell if a turn-signal bulb has blown because the flashing frequency greatly speeds up. This is because the flasher has lost half of the "load", which keeps it at the right tempo. The effect is exaggerated if, for example, you replace two 21 watt stock turn signals (one per side) with two LED turn signals, each with 1.5 watts. Now the load on the original flasher is only 3 watts (2 x 1.5) instead of 42 watts (2 x 21). This won't work.

There are two ways to solve the problem: You either install a special LED flasher, or you "fool" the original flasher into thinking the LEDs have the correct wattage by installing electrical resistors. And by the way: flashing frequencies of 90 flashes per minute (tolerance of plus/minus 30) are legal.

The simpler option, namely to replace the relay, is only possible under certain conditions:

  • Two separate indicator lights for left/right turn signals (not a single one for both sides) on the instrument panel
  • There must be no turn signal beeper or a hazard warning flasher already installed
  • The original relay must not be integrated in a multifunctional electronics unit (this is the case if there are more than three cable outlets).

Once you have checked the above, you'll know which option is for you: relay replacement or fitting resistors.

How to install LED turn signals

[IMAGE: signals with an "E" mark.]
Important: Only use turn signals with an "E" mark

Condition for approval: Turn signals with "E" mark

When buying turn signals, make absolutely sure that the lenses have an "E" mark so they do not have to be specially entered in the vehicle documents. Approved "front" turn signals bear the code 1, 1a, 1b or 11, and approved "rear" turn signals bear the code 2, 2a, 2b or 12 (see Fig. 2). Most turn signals in the Louis range are approved for both front and rear, so have two codes. If you have a choice of turn signals with stalks of different lengths, please bear the following in mind: under EU rules front turn signals must be at least 240 mm apart, rear turn signals at least 180 mm.

[IMAGE: relay.]
Vital for the relay: correct polarity

If you are changing the relay, simply skip the step described below for installing the resistors. The flasher with order no. 10033844 always flashes at the same frequency with a load of between 1 and 30 watts; in other words it is load-independent. The flasher can only be installed under the conditions described above. Ensure that the polarity of the relay is correct – incorrect connection will immediately destroy the relay electronics and void any manufacturer's warranty. 

Take special care: Even if the arrangement of connections is the same as in the original relay, the polarity may still be different. Always check the polarity with an LED test light first (to do so, follow the flasher installation instructions). If the plug-in connectors do not fit, it is relatively easy to make adapter cables to save you having to cut off the original connectors on the wiring harness.

Unfortunately, almost every vehicle manufacturer now uses turn signal bulbs with different wattages. So a turn signal could be 10, 18 or 21 watts. The wattages are also vary with LED turn signals. But since the stock flasher has to be fooled into thinking that a bulb with the correct (standard) wattage is fitted, you need to do a bit of research and a small calculation before writing your shopping list.

In a word:

  • Find the wattage of a bulb from the original turn signal (shown on the lens) and multiply by 2.
  • Find the wattage of one of your chosen LED turn signals and multiply by 2.
  • Subtract one from the other and select a resistor closest to the difference.
[IMAGE: led turn signals.]
4 LED turn signals, 2 resistors, 4 adapter cables, mount cover

On a Kawa Z 750, we demonstrate what to fit, and how best to do it (see Fig. 4). The LED turn signals we are using are curved, which is why there is one model for front left and rear right and another for front right and rear left.

Based on the formula above, we calculated the resistors to be used:

  • A stock turn signal is 10 watts, x 2 = 20 watts
  • An LED turn signal is 1.5 watts, x 2 = 3 watts
  • Difference between the two values: 17 watts

The ready-made adapter cables, which are available for many different Kawasaki models in the Louis range, come in pretty handy. They fit directly onto the compact connectors of the wiring harness on the bike, and the other connectors fit to the resistors or turn signals without any modification. Of course, when you remove original turn signals, you're left with unsightly holes almost big enough to throw the new mini turn signals through. This is where the turn signal mount covers come in handy. These covers are not specifically designed for the Z 750 but fit just fine. If you cannot find something suitable for your motorbike, you can make a cover out of aluminium, plastic or sheet metal.

Installing LED turn signals

[IMAGE: cockpit fairing.]
Remove cockpit fairing

As with all work on the bike's electrical system, the negative cable must first be disconnected from the battery to avoid a short-circuit. To replace the front turn signals, take off the front fairing and set it down in a safe place (on a cloth or blanket).

[IMAGE: mount cover.]
Mount covers are a ready-made solution

Now you can remove the original turn signals and screw on the new ones including the mount covers. When tightening them, remember they are not truck wheel bolts, so don't use too much elbow grease. Incidentally, mini turn signals often have a fine thread M10 x 1.25 (standard nuts are M10 x 1.5). So if you lose a nut underneath the workbench, please order a replacement.

[IMAGE: adapter cables.]
Adapter cables leave the wiring harness intact

Next, connect up adapter and turn signal cables. Remember: LED turn signals will only work if the polarity is correct. Since vehicle manufacturers do not use standardised cable colours, a wiring diagram, if you can find one, will help you locate the positive or negative cable; otherwise, simply try out both possibilities – doing so will not break the LED turn signals. Proceed in the same way for the other side and then you can put the fairing back on. The cross-head screws all engage in plastic threads, so take care or else you will damage them.

[IMAGE: tail fairing.]
Take off tail fairing and remove turn signals

To fit the rear turn signals and resistors, take off the seat and unscrew the tail fairing. Once again, carefully set down this expensive and delicate piece of plastic.

[IMAGE: turn signal, resistor, adapter cable.]
Correctly wired: turn signal, resistor, adapter cable

Like before, remove the rear turn signals, and fit the new mini turn signals and the mount covers. The turn signal cables are routed similarly to the original ones.

Installing the resistors

[IMAGE: resistor connection.]
Resistor connection at the rear

Now fit the resistors. These are already pre-wired in parallel. The resistors have no polarity, so it doesn't matter which way round they go. The cable terminals provided for the Louis resistors make fitting easy. If you need 2 resistors per side, they can both be connected at the rear turn signal (usually more space).

[IMAGE: resistors fitted underneath the seat.]
Resistors fitted underneath the seat

But first you must decide on a suitable place to fit the resistors, as they can heat up to over 100°C in operation (with long signalling or using your hazard warning lights if you break down), so they need a little cooling air. They should not be completely enclosed or mounted in direct contact with a plastic surface. It's a good idea to make a little mount plate out of sheet aluminium and place that in the bike. The Z 750 has a metal plate on the right next to the control unit, which is an ideal place to install it. This is where we fitted the resistor for the right turn-signal circuit using 3 mm nuts and bolts. We fitted the resistor for the left turn-signal circuit on the left side next to the control unit.

However, the resistor cannot be screwed directly to the visible metal plate on this side, as there is another control unit underneath the plate, which could get damaged. We screwed the resistor to a metal plate and inserted the whole thing under the black box. As long as you bear in mind that the resistors can heat up, there are other positions where they could be secured.

Following installation: Turn signal test

[IMAGE: infrared thermometer.]
Infrared thermometer reads 79°C after a few minutes

Once you have wired and connected them (don't forget the battery earth cable), you can do a test run. We monitored the temperature of the resistors with an infrared thermometer. They heat up to almost 80°C in just a few minutes. So never attach the resistors with double-sided adhesive tape, for example in the fairing. The double-sided adhesive tape will come away in the heat and the plastic will deform or melt. If everything is working, you can put the tail fairing back on, and you're done!

[IMAGE: multifunctional crimping tool.]
Multifunctional crimping tool for Japanese connectors without coloured markings

If you cannot use adapter cables, it is important to establish a safe, permanent cable connection. One option is to solder the cables and then to insulate them with heat shrink tubing; another is to use crimp-type cable terminals. For this, Japanese connectors should be used, for which a special crimping tool is required. Both are also available in the professional set.

Which resistances for which conversion?

table of resistors

If a different resistor is required in special cases, ask in an electronics store for a resistor with heat sink for use with your wattage.

Values of the individual resistors:

  • Order no. 10032205: 10 Ohm, „replaced” 14,4 Watt
  • Order no. 10032063: 8,2 Ohm, „replaced” 18 Watt
  • Order no. 10032089: 7,5 Ohm, „replaced” 19,2 Watt
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Download this tip

For the garage: Simply download, print out and take it with you.

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the experts

The Louis Technical Centre

Problems getting spare parts? Or maybe you've got a technical question about your motorcycle or an accessory The Louis Technical Centre can help! Remember to quote all the necessary details of your vehicle – better still, send us a copy of your registration document.

We will get back to you as quickly as possible!

So: send us your technical problem!

Please note!

These tips for DIY mechanics contain general recommendations that may not apply to all vehicles or all individual components. As local conditions may vary considerably, we are unable to guarantee the correctness of information in these tips for DIY mechanics.

Thank you for your understanding.

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