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The issue of using aftermarket LED turn indicators retuning fast flash rates keeps returning to this forum time and time again and has prompted me to provide a solution, as I have once before.
But first a quick rundown on why flash rates increase. The flash rate of the turn indicators is to tell you, the rider, that one or both of your indicators is not working. The controlling relay, whether it be mechanical or electronic, detects that there is a decrease in current as both indicators (front and rear of one side) are wired in parallel.
Aftermarket turn indicators tend to draw LESS current than the original manufacturers equipment.
To remedy this is to make the circuit draw MORE current than the aftermarket LEDs are drawing.
A bit of electronics theory is appropriate here: the current in a circuit is equal to the voltage applied divided by the resistance of the circuit. I=V/R where I is current in amps, V is voltage in volts, and R is resistance in ohms.
Power dissipation of a circuit is equal to the voltage applied squared divided by the resistance of the circuit. P=VxV/R.
LEDs draw very little current compared with incandescent bulbs because their resistance is greater.
So if you fit aftermarket LED turn indicators and they cause your flash rate to increase it is because their resistance is higher which therefore draws less circuit current and the relay thinks there is a problem.
How do we fix this?
Simple, we add a resistor in PARALLEL with the indicator to draw more circuit current. i.e. across the indicator leads.
But how do we know what value of resistor to use? Forget all you hear about calculating the value (ohms).
For those with some hand skills and a multimeter a simple method is at hand.

Place a variable resistor (potentiometer), a trim pot will suffice, of 500 ohms, or greater, across the two leads of the turn indicator fitted to the bike with alligator clips, if you have them.
Connect the wiper of the pot to one lead of the indicator and one end of the pot track to the other lead. Polarity is not important.
Set the wiper of the pot to the free end of the track to provide max resistance. Now switch on power to the bike and select that side indicator to on.
As the LED flashes, slowly turn the pot towards the end that is connected to the indicator until the flash rate slows to what it should be. Switch of turn indicator and bike power. Disconnect the pot from the bike noting which pins of the pot were used.
Measure the resistance across those two pins with the multimeter. You now have the value of resistance that the circuit needs in order to draw the correct amount of current.
But there is a small problem with this resistance value. Resistors are manufactured in 'preferred values' and it is most likely that a cheap 10% tolerance resistor is not available in that exact value. So select the closest value resistor that is LESS than your measured resistance.
But this is not the end for you just yet, you now need to calculate the correct wattage of the resistor. The resistor's wattage is the power i.e. heat, that it can continually dissipate.
Using the power formula previously mentioned you can calculate the wattage of the resistor. So, if your resistor value as determined above ends up to be 120 ohms and the voltage applied across the resistor is 12 volts, 12x12/120=1.2 watts.
Again you will not get a 1.2 watt resistor but you can get a 2 watt resistor.
Unlike the selected resistor value, for the selected wattage rating choose the closest HIGHER.
Your resistor wattage (power) is for continuous use, but your turn indicator flash rate is intermittent and for a relatively short duration so you would get away with using a 1 watt resistor, the smaller the wattage the smaller the physical size therefore the easier to hide.
So for this example when you go to buy resistors for your new after market rear LED turn indicators you will ask for: qty two, 120 ohm 10% 1 watt resistors, or if you want to be safe 2 watt. The 10% tolerance means the actual resistor value (ohms) will be + or - 10% of the 120 ohms.

There are plenty of on line tutorial on electrical and electronic circuits that explain how things work, and the correct terminology.
 

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…. Or you can buy kellerman Rhombus extreme and save the extra work.
 

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.... or you can apply the same theory to changing stock LED indicators with aftermarket LED indicators, realise that isn't the issue, and continue scratching your head.
 
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