Any - Additional stop/tail/number plate light

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Wed 1 Oct 2014 18:17
Any - Additional stop/tail/number plate light - Cris_on_the_gas

Have tried 3 light units so far and all display the same problem. I am trying to connect additional stop/tail light which also has numberplate light included. When it's wired up with the existing lighting only the number plate light works and the tail light darkens. The brake light works OK. All of the units have been e marked.

I have tried separate 12V supply direct from battery for tail light but as soon as other stop/tail bulb inserted the tail light darkens but the number plate light stays on. Unit has 3 wires connected, stop(Red). tail/numberplate(Yellow). and earth(Black).

To me it seems that if a resistance to earth is seen through the brake light filament then the tail light is extinguished. As tail light is extinguished even if brake is not applied.

Strange that i have had 3 lights all display the same symptom. All have been LED lights.

any ideas?

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Wed 1 Oct 2014 18:25
Any - Additional stop/tail/number plate light - Cris_on_the_gas

Should have said this is on a motorbike, existing number plate light has been replaced with additional stop/tail and number plate light. Existing rear light remains

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Wed 1 Oct 2014 19:24
Any - Additional stop/tail/number plate light - mss1tw

Test with a normal lamp as LEDs are polarity sensitive.

I had to home make a rectifier to use an LED indicator dashboard light on my bike as the polarity was switched for left/right operation - so it would only work one way!

Edited by mss1tw on 01/10/2014 at 19:24

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Thu 2 Oct 2014 09:31
Any - Additional stop/tail/number plate light - Cris_on_the_gas

It's wired up right as light works but only if other bulb is removed.

It's stop and tail light not indicator

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Thu 2 Oct 2014 14:46
Any - Additional stop/tail/number plate light - mss1tw

I'm standing by my assertion that LED lamps can behave in weird ways on vehicles, and if possible the easiest thing to check is whether a good old filament lamp behaves the same way.

But then I'm only an electrician by trade who rewired the front end of his motorbike and had strange LED problems......

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Thu 2 Oct 2014 17:02
Any - Additional stop/tail/number plate light - Cris_on_the_gas

I'm standing by my assertion that LED lamps can behave in weird ways on vehicles, and if possible the easiest thing to check is whether a good old filament lamp behaves the same way.

That may be the case but I am trying to fiond out why. If I put 2 filament lamps in parallel then they both light up.

What I am trying to find out is why an LED light unit behaves in this way and how this can be overcome. I would like to have 2 rear lights on the bike.

The supplier has offered full refund on light unit but replacement will just come with same issue and can't find a filament fitting that looks as good as LED unit

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Thu 2 Oct 2014 17:23
Any - Additional stop/tail/number plate light - mss1tw

That may be the case but I am trying to fiond out why. If I put 2 filament lamps in parallel then they both light up.

What I am trying to find out is why an LED light unit behaves in this way and how this can be overcome. I would like to have 2 rear lights on the bike.

The supplier has offered full refund on light unit but replacement will just come with same issue and can't find a filament fitting that looks as good as LED unit

So the filament lamps work as you'd like the LEDs to?

Is the new unit sealed or is it possible to reverse the leads going to the lamp that doesn't work?

As they are a diode, not only do they not work if the wrong way round but will block all current flow on that circuit.

Why the polarity would be different I don't know but if you're getting a resistance to earth and a light out, without looking at it I'd start there.

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Fri 3 Oct 2014 10:47
Any - Additional stop/tail/number plate light - Cris_on_the_gas

No it's not that.

Unit has 3 wires. 1 wire for tail and numberplate light. 1 wire for brake light. 1 wire for earth.

With tail and earth lead connected tail light and number plate light are illuminated. Simple battery and earth connection.

When brake light wire is connected, ( no voltage as brake light switch not operated, the rear light dims to nothing but the 3 LED's for the number plate light stay illuminated.

Only thing I can think of is that there must be asensor on the brake light lead if it sees a resistance to earth through the filament of the other bulb it extinguishes the LED's of the tail light. Cannot understand why a manufacturer would do such a thing.

So I want the tail and number plate light to illuminate when 12 V applied to supply and earth connected to earth wire. Shouldn't be too much to ask

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Fri 3 Oct 2014 11:23
Any - Additional stop/tail/number plate light - dieselnut

The previous BMW motorcycle I had used fillament lamps & had a detection system that would bring up a warning on the dash of any lamp failure.

Also if the rear running lamp fillament failed it would automatically illuminate the stop lamp so you had some rear illumination, quite clever I thought.

LED lamps consume a lot less current, so if your bike has this detection system it might think you have a failed lamp.

I would try temporarily wiring both the old fillament lamps & new LED lamps in parallel & see if they both work ok like that.

If so, you will need to get some resistors to wire in parallel with the LED lamps to increase the current to the same as fillament lamps to fool the lamp detection system.

Edit. I've just looked at your first post again & it looks like you might have already tried this.

It could be that your new LED lamps already have resistors in them & the extra current is causing problems. My current BMW has load sensing instead of fuses. If it senses too much current is being drawn it will shut down that circuit until the fault is cleared.

Just a thought.

Edited by dieselnut on 03/10/2014 at 11:37

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Fri 3 Oct 2014 11:42
Any - Additional stop/tail/number plate light - Cris_on_the_gas

It's not a BMW and is not using CAN BUS. I am familar with CAN BUS.

I have tried wiring the existing light and new LED light in parallel and they do not work for reasons stated above. Actually that is exactly what I want to do.

Can't see how putting resistors in paralle will help. With open circuit on brake light supply it works correctly putting resistance i.e a filament light in parallel stops it working. so putting less resistance with parallel resistors is not going to work

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Fri 3 Oct 2014 12:20
Any - Additional stop/tail/number plate light - mss1tw

What bike is it?

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Fri 3 Oct 2014 16:09
Any - Additional stop/tail/number plate light - Cris_on_the_gas

It's a Yamaha Fazer 1000.

Because it has luggage fitted I have fitted an additional rear light unit where the existing number plate light was. So I want to have additional tail and stop lamp

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Fri 3 Oct 2014 16:14
Any - Additional stop/tail/number plate light - mss1tw

Can you try running a seperate earth directly from the rear lights 'sub frame' to your unit and seeing what happens?

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Sat 4 Oct 2014 15:06
Any - Additional stop/tail/number plate light - Bolt

Correct me if wrong but don`t they have a circuit inside led lamp unit that controls voltage to led s, if the voltage isnt kept within limits the diode loses brightness by about 2/3rds

I have come across faulty ones where there is a circuit problem,nothing you can do about it, but a replacement may be ok

LED lamps are strange at times

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Mon 6 Oct 2014 13:00
Any - Additional stop/tail/number plate light - Cris_on_the_gas

Can you try running a seperate earth directly from the rear lights 'sub frame' to your unit and seeing what happens?

Exactly same result

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