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SHUNT mod for LED lights question?

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SHUNT mod for LED lights question?

Post by darylrobert » Fri Oct 25, 2019 4:27 am

Ive installed two philips 4w red LEDs to my brake lights. The colour and brightness is identical to the halogen, only plus is the quick responce time and low current draw and ive found that with the correct resistance i can avoid error messages but it can still detect if i unplug an LED. There is no heat on the shunt after 5minutes with LEDs or without LEDs (failure mode)

On my vehicle the 3rd factory LED brake light does not trigger a warning when unplugged

Question is , is unplugging a LED a good failure test?....does anyone have a failed LED to test, does it still draw a current??
LED brake lights V70.jpg
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Re: SHUNT mod for LED lights question?

Post by ndphotonl » Sun Oct 27, 2019 3:07 pm

Does this work? I still want to do this to my S80.

Did you break out a whole piece of the shunt where the resistor goes or?

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Re: SHUNT mod for LED lights question?

Post by Sardine » Sun Oct 27, 2019 5:40 pm

Hi DarylRobert, I don't really know the answer to your question but I suspect the correct answer is no, a failed led will not draw a current.
Could you do a post on how you did it, the LED you use etc?
For me, the most significant plus is not having to keep replacing blown brake lights.

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Re: SHUNT mod for LED lights question?

Post by EngineeringBloke » Fri Nov 01, 2019 11:22 am

You replaced two regular brake bulbs with LED ones. They came with resistors and when either one is disconnected, the bulb fail warning is shown.

So this seems quite successful. But when you tried disconnecting the high LED brake light and you got no warning.

Here is a test you can do:
Replace the original brake bulbs again and disconnect the high brake LED.
Do you get a warning?

I suspect that you will not and that you have not broken the detection with your LED replacements. If you do see a warning in this case, it means that the resistance in the replacement LEDs is too low and that those two resistors allow more current that the original setup. You could try replacing the resistors with slightly higher ones but I would not bother myself.

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