LED/Electrical problem

[paul richards]

I decided to replace my high level LED brake light with 2 round LED lights. The new lights (cheap and made in China - isn't everything) are designed for use on a motorcycle as side and brake light. My original intention was simply to wire them up as brake lights but there is a reasonable distinction between the side and stop illumination so I decided to use them as intended for side and stop bearing in mind Caterham rear lights are quite poor (even with my JAL conversion).
Im no electrician but have a basic understanding and have wired them up using the sub loom I already had for my existing brake light and connected the new side lights to the correct feed in the harness for the rear side light. Existing side lights and new additional side lights work as expected. When ignition is on all side lights and brake lights (including all the new lights) work as expected. However when side lights are on and ignition is switched off the new high level brake lights go out when I press the brake pedal. I have replaced the new LED lights with "ordinary" lights and they work fine. Seems to be something within the new LED lights. I can of course simply ignore this and live with them as under normal use there is no real problem, but why they do this is bugging me. Any ideas.

[Jonathan Kay]

"When ignition is on all side lights and brake lights (including all the new lights) work as expected. However when side lights are on and ignition is switched off the new high level brake lights go out when I press the brake pedal."

I don't understand... why do they "go out". Were they ON before you pressed the brake pedal?

...

Do the new lamps have resistors and diodes built into the unit or do you have to add them?

Do you have a multimeter?

Jonathan

[jbcollier]

He says, ignition off, sidelights on, and the new, high-level, lights (with sidelight function) go off when he steps on the brake.

What is happening is that the non-powered, brake light circuit is providing an alternate path to ground for the side light voltage.  Not quite shorting it to ground but enough to lower the voltage below the LEDs active threshold, extinguishing the light.

You could wire in diodes but, really, does it matter that much?  You have sidelight function and brake light function and when are you ever parked up, sidelights on, ignition off and your foot on the brake?

[Jonathan Kay]

Thanks.

Yes, sounds like alternative circuit. 

And I've corrected the component! : - )

Jonathan

[John Vine]

#3  Makes sense, but should brake lights ever come on when the ignition is off? 

Also, I'm wondering if there could be problems at MOT time.  I guess a lot would depend on how picky the tester is regarding the entire stop-lamp set-up?  From the MOT Manual:

4.3.2. Switching

All stop lamps must light up immediately when the brake is applied and switch off immediately when the brake is released.

Additional stop lamps, over and above the mandatory requirements, must be tested.  However, if you are not sure that they’re connected, you should give the benefit of the doubt.

Defect                                                                                                        Category

(iii) remain on when the brakes are released                                             Dangerous

4.3.3. Compliance with requirements

Press the brake pedal to light up the stop lamps and operate all the other lamps in turn to see if the stop lamps are adversely affected.

Defect                                                                                                        Category

(b) A stop lamp adversely affected by the operation of any other lamp        Major

 

JV

[paul richards]

I think I badly worded it. I said :-

""However when side lights are on and ignition is switched off the new high level brake lights go out when I press the brake pedal."

I should have said high level side lights go out when I press the brake pedal. 

I think you are correct jbcollier. An alternative route is being found. I did think a diode would be the answer but wouldn't know how to go about it. The lights are certainly working satisfactory for use and I can live with it, but it was just puzzling me. 
Thanks all for your replies. 

[SM25T]

Polarity connection ok ? LEDs have to have correct polarity of course 

[paul richards]

Yes. Polarity is fine. In my experience if polarity is wrong they don't work at all. 

[John Vine]

#6  Thanks for the clarification.

JV

[David aka Blue7]

>>"Caterham rear lights are quite poor (even with my JAL conversion"

I find that statement puzzling, my JAL led conversion is incredibly bright both side and brake lights ... when did you last wash your car Paul?

[paul richards]

Car is nice and clean and JAL lights are much better than standard but are still not as good as many tin tops. I certainly felt vulnerable with standard lights and anything that makes me more noticeable is a good thing. 

[David aka Blue7]

Fair comment.  Unless driving at night or in adverse weather conditions, I think drivers at the rear probably notice the bright colour of the car before any lighting.  I also think that the biggest danger nowadays is the mobile phone, drivers texting or using social media while driving, so even rear spotlights won't protect you from those people.  One of the commonest sights I see is delivery drivers driving away from my house looking down at their phones and messaging  back to base with a photo of the item left on my doorstep and confirming delivery.  When I am a passenger I sometimes indulge in the game of "spot the driver on their mobile" and I recall one occasion when I counted 5 in a row!

[jbcollier]

My 69 Seven S3 has no roll bar and anemic rear lighting.  As I drive my cars in all weathers, I added a rainlight with a brake light option:

Here's a video of the rain light function:

And the "third" brake light:

The rain light also doubles as a hazard light.  Both are INCREDIBLY bright compared to the stopck lights with LED bulbs.