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Discussion Starter #1
Hi, got these LED lamps to replace the normal dual filament bulbs for stop/tail function and cant understand whats happening. I test the LED's on my battery booster with earth and a wire to tail light contact =ok, then wire to brake side contact = ok and also tail on + brake on. All ok. Put the bulbs in Trafic vehicle [08 reg] and all goes bonk. Turn lights on, and brake side of LED lights up. Turn lights off and depress brake pedal and brake lamp lights up ok, so a conflict. Changed wires round but still no good. Put my tester on the wires and found that when lights are on there's 12v at tail side of LED and also 3 volt on Brake side, so there's a voltage leak across the bulb [or is there] to the brake side and therefore illuminating it. Or is the voltage coming from somewhere else? Worked ok on the battery booster but not in the van. Confused. Graeme.:mad::devil::confused: ps these are canbus type bulbs
 

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Did you try testing with the original bulbs in to see if there was 3v in the brake connect with the tail lights on?.

Its a triple connect bulb so 2 + and the neg and the negative are in close proximity.

I wonder how is the canbus connected up internally.
Externally you connect a resistor across the + and neg wires as close to the bukb as possible.
Is there a resistor for each circuit internally?

Does the traffic have a hi lvl led brake light of some sort?
Does that glow when the tail lights are turned on?.
Any led bulbs i fitted in 21 w or higher circuits in my renault didnt work out so well, .
Fog light leds for example, front and back,one side lit fine, the other had a bare glow (without resistors and non canbus).

Try a differnt bulbor rewire to have either the brake or sidelight in the dual filament socket and mount the other elsewhere or make up your own interior dual filament socket(a 3rd brake and taillight socket with a normal bulb in),wire it into the circuit and put it behind a cover.That might soak up any residual current.

Those suggestions might sound like rubbish but thas all I can think of..without messing around with external resistors, and since the 2 circuits have a common return in the bulb housing , might not do any good.
 

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Hi, have finally fixed this problem. You are right, the common thing between the two bulbholder connections is the earth wire. With this canbus bulb in [which has internal resistors] I had to eliminate any voltage going to the brake side of the bulb. Did this by soldering in a diode [IN4004] on the earth wire. Also put a diode [same type] into the brake side feed. So theres no voltage going to the brake side from the side lamp and no voltage going back up to the brake pedal.. All works ok now. grstools.
 

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@grstools, it is important that you isolate all the connections. What seems to be the issue here is that the different connections coming from tail and brake are not properly wired. Make sure there is one common ground all the wiring is going to and then step-wise move on to inspecting the brake switch. First turn on the brake and inspect voltages across both tail and brake light wiring ends, then see the tail light voltage. I suspect there will be a grounding issue and it’ll be resolved pretty quickly. Please let us know what you found out though.
 
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