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Premium Member
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Discussion Starter #1
I converted my 85RS to a scrambler. One change was the replacement of the stock tail light assembly with a LED running/brake/license light combo. My issue is the rear light monitor light in the instrument cluster won't go out when the front and rear brakes are used. I am guessing the LEDs aren't drawing enough power. I can always pull the bulb, but I like that monitor. It has drawn my attention to rear light problems many times. What is the solution? My knowledge of electronics is limited. I can do very basic soldering; so, I could put a transistor of some sort on one of the rear light wires if I knew which wire and which transistor.

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Jon
 

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Addict
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3,750 Posts
Yours is a common problem with vehicles that have a bulb failure monitor when led lights taking very little current are fitted. The simple bulb failure circuit monitors the current flowing through a good bulb and that keeps the fault light out.

At its simplest level, one solution is to fit a resistor across the led light so the bike thinks the bulb is still there. These monitors can work in different ways. The most difficult is the system that needs to see the full bulb current to keep the light out. You would need to get a bulb of the same wattage and wire this to your led rear light which somewhat defeats the object. You could also use a resistor with a big wattage but that will get hot!

Often these circuits will put off the warning light when a current less than the bulb rating is present. How much less depends on some tests you would have to do first. Find out the wattage of the rear bulb you took out, then try adding a lower wattage bulb across your led light to to find out the LOWEST wattage that can make the warning light go out.

Lets say you find a 6 watt lamp would turn off the warning lamp. You could then go buy a 30 ohm 6 watt resistor and wire that to your rear lamp wiring and mount it somewhere where it would not burn anything. If a 12 watt bulb turns off the warning, then you would need a 15 ohm 12 watt resistor etc.

These are the type of high wattage resistors to use which can be fixed to a flat metal surface somewhere on the bike.

http://uk.rs-online.com/web/p/panel-mount-fixed-resistors/1073188/



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PsyKotic Waterfowl
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Putting in a load resistor in parallel defeats the purpose of having a bulb monitor because it will always "see" the load resistor as a good filament. Also, for the taillight, since it is always on, the load resistor will need to be mounted somewhere where it can dissipate the heat that it generates. Even though the bulb monitoring feature will be disabled, the testing of the two brake switches at startup will probably still work.

I run all of my Ks with LED brake and tail lights. My solution, since LEDs last "forever," is to just get rid of the bulb monitor altogether. At it's connector in the left side of the relay box under the tank:

Short the front brake switch wire(Gray/Red) and the rear brake switch wire(Gray/Green) to the rear brake light(Gray/Yellow.)

Short the tail light power(gray/white) to the tail light wire(Gray/Black)
 

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Premium Member
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Discussion Starter #4
FlyingDuck said:
I run all of my Ks with LED brake and tail lights. My solution, since LEDs last "forever," is to just get rid of the bulb monitor altogether. At it's connector in the left side of the relay box under the tank:
Thanks for the tips. I am back on the road after replacing the plugs and fuel pump relay. I finally decided to pull the bulb on the dash. About 10 minutes of work. Now I need to break myself of the habit of hitting the front and rear brakes on start up.


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Jon
 
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