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Bensonboo

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A dc question if possible, I have a motorbike with a 3 wire led side / brake light. I was planning to add another led light to purely act as a supplementary brake light. When I checked the wires, I have 8v on one wire, (the rear light) 12v on another wire, (the brake light) only when pressed, and a ground wire. I planned to spur off of the 12v wire and ground but when I did i find the supplementary brake led acts like the existing, i.e. it receives 8v with side lights and brightens when brake pressed. How can I make it function purely as a brake light?
 
Took me a while to figure this out - the existing lamp is LED to start with ?
My guess is that internally there is only one set of LEDs, fed via a resistor for low brightness (tail light) and direct for high brightness (brake). So I'd expect the brake light wire to be "live" but at some less than 12V voltage when the tail light is on - but since there's just a switch at the other end, this backfeeding won't matter.
One way to fix this would be to put a suitably rated diode in series with the brake light wire so that it can't backfeed and then your additional brake light (connected on the switch side of the diode) will work normally.
 
Hi, thanks, I'll try to be more detailed. It is one set of LED's in the light, it has 3 wires going to it, green, white and brown. When lights are off and you brake, the white carries 12v. When you just switch the lights on, the brown carries 8v. When you have the lights on and brake, they both carry 12v. I dont want to alter the function of the original light, (side light and brake light), I just wanted to add an extra brake light. Thanks again.
 

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