LED headlight makes run rough - Wrist Twisters
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post #1 of 6 Old 03-12-2019, 02:36 AM Thread Starter
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LED headlight makes run rough


I have a 2005 fuel injected Hornet 919 with PC3.

I just installed the LED headlight below and when it's plugged in it makes the bike run rough on idle, sometimes cuts out. If I unplug it's instantly fine! Some weird circuitry load issue? Not a big deal as I can use a different light but interested to know what the issue could be so I can get a new LED light that doesn't mess things up.


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post #2 of 6 Old 03-12-2019, 09:21 AM
(Quintus) Pilus Prior
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Their documentation leaves a bit to be desired, but I would guess it's drawing too much power. If you have the ability I'd try to measure how much current it's drawing. I was going to try to calculate how much it claims to use, but it specs AC as the input power and then specifically says that it can only be used on a DC motorcycle, so I'm not sure what values correlate to what.

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post #3 of 6 Old 03-12-2019, 10:27 AM
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I'd say it's unlikely that the designed power consumption is a problem, even if it was 3 times what they have listed. I'm no expert by any means, but my guess would be that there's an issue with the LED driver circuitry, causing it to either put too much load on the system (shorting?) or somehow causing some feedback into the electrical system and messing with the ECU. Does it put out decent light when plugged in?

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post #4 of 6 Old 03-12-2019, 12:50 PM
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I know you unplugged it and said it was fine, but did you try putting the stock bulb back in too? If it still has rough idle with stock bulb, then my guess is alternator or regulator, but that's unlikely since it was running fine before the swap.

Also, did you check if it's grounded correctly? (Not sure about the 919, but sometimes low beam is a lower voltage than high beam, thus, there would still be a potential difference b/w the two leads, so if the two leads are connected in the right(wrong) order, the LED might still run, but would probably cause issues with ECU).

Like Badmoon said, those specs for the LED driver are all over the place. It could very well be a load issue if the driver is faulty and not blowing the fuse for some reason. Could also be a feedback issue

Not an expert, but here are some tips:
Check battery voltage difference b/w stock bulb and LED (with the bike running)
Check your Grounds
Check the current draw of the LED
Check alternator and regulator
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post #5 of 6 Old 03-12-2019, 10:44 PM
(Quintus) Pilus Prior
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Wow < $20 for an LED. I wonder how good it is.

I thought one of the big things about LED was that it used a lot less power.

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post #6 of 6 Old 03-25-2019, 03:17 AM
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Check your wiring for a leak to ground and if you removed and replaced connectors then check for a loose ground. Test meters are great, but also pull on the harnesses while running and see if anything changes, then snug down, isolate, whatever. If this does not help at all, then that is normal for my advice! Good luck, and not to worry as you will locate it.

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