Rear brake light warning - light works. Baffled

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Stuckmojo
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As per title, G55 AMG, I got this read brake light (3rd Brake Light) on dash warning. I had a mate press the brake pedal, the light works as well as the other two. I'm stumped. 

Thoughts? 

 

 

Pistonhead
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Re: Rear brake light warning - light works. Baffled

The brake warning light system is sensitive appartus. It is not mandatory that a bulb(s) has to be physicaly out or blown to activate the sensor. It can activate if you are close to a bulb(s) about to blow. 

Check and replace all brake light bulbs to reticfy your issue. If you notice the glass bulb blacking on its inside the illuminating wire of the bulb has excessive oxidised and nearing its end of life. The sensor picks up on the current drawn and if it sensens a differential imbalance of currents between all bulbs, it activate's a blown bulb. 

Stuckmojo
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Re: Rear brake light warning - light works. Baffled

Thanks for the reply. As it happens, the warning light went away by itself. I'll keep an eye out for it. 

Pistonhead
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Re: Rear brake light warning - light works. Baffled

Another plausable reason is that ther could have been a momentary vibration causing a circuit to break or cause high resistance triggering the warning light - extremely unlikely but theoretically possible.