LED tail/stop bulb connundrum

[Roger J]

Some time ago I fitted LED bulbs to the stop/tail and front sidelights on my 12v Ruby. Recently, as I drove into the darkened garage, I noticed that the front side lights were coming on as I braked. Eventually found that the corncob type LED tail/stop bulbs were responsible.
On investigating I found that all of the individual |LEDs in the bulbs come on for both tail and stop function - but in tail lamp mode they are all dimmer.
There seems to be some kind of internal connection between the tail and stop pips which is allowing brake lamp voltage back out onto the side lamp circuits.
I cannot detect a resistance but suspect maybe a zener diode with poor reverse resistance..I put back the the old incandescent bulbs and all's well again.
I wondered if anyone else has come across this  - or has any other theories.

[Alastair]

I've quite literally just come in from attempting to fit LED stop/tail bulbs to the Ruby (6v) in time for our regular Tuesday night run but could not get them to work properly. I've had LED front sidelamps for some time and had no problem with them.
The rear LEDs will not work as pairs - I can get stop one side and tail the other and have tried swapping wires around with no success, so I've given up and have also returned to incandescents for the time being...
I'll have another go tomorrow and report back, but would be interested to hear what others think.
Alastair

[Roland Alcock]

I just checked mine (same configuration) and front sidelights do not come on. However my led flashers don't light or sound the repeater/buzzer when the brake lights are on, but do continue to flash.

I shall try another flasher unit sometime to,see if that makes a difference.

Roly

[Charles Levien]

I've quite literally just come in from attempting to fit LED stop/tail bulbs to the Ruby (6v) in time for our regular Tuesday night run but could not get them to work properly. I've had LED front sidelamps for some time and had no problem with them.
The rear LEDs will not work as pairs - I can get stop one side and tail the other and have tried swapping wires around with no success, so I've given up and have also returned to incandescents for the time being...
I'll have another go tomorrow and report back, but would be interested to hear what others think.
Alastair

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Hi Alistair,

You may find the answer lies in providing a dedicated earth for each lamp.

I have LEDs on my Opal ( six volts ) and they work extremely well.

Charles

[Alastair]

Thanks Charles - I'll give that a try tomorrow. I did wonder whether it was an earthing problem - but it just occurred to me that I've still got incandescents in the pork pie lamp which may be upsetting things...
Alastair

[Charles Levien]

Thanks Charles - I'll give that a try tomorrow. I did wonder whether it was an earthing problem - but it just occurred to me that I've still got incandescents in the pork pie lamp which may be upsetting things...
Alastair

Good luck tomorrow then and sorry I spelt you name wrongly.

Charles

[Alastair]

Thanks again and don't worry about the name - my surname, Wreford, causes even more confusion!
Alastair

[Bill Dixon]

Some time ago I fitted LED bulbs to the stop/tail and front sidelights on my 12v Ruby. Recently, as I drove into the darkened garage, I noticed that the front side lights were coming on as I braked. Eventually found that the corncob type LED tail/stop bulbs were responsible.
On investigating I found that all of the individual |LEDs in the bulbs come on for both tail and stop function - but in tail lamp mode they are all dimmer.
There seems to be some kind of internal connection between the tail and stop pips which is allowing brake lamp voltage back out onto the side lamp circuits.
I cannot detect a resistance but suspect maybe a zener diode with poor reverse resistance..I put back the the old incandescent bulbs and all's well again.
I wondered if anyone else has come across this  - or has any other theories.

Roger,
 The problem you have with the LED lamps could be down to poor earths.
 Run separate earths from the lamp unit bodies to a good chassis connection, you are dealing with semiconductors they have different characteristics
 to filament lamps.Hope this solves the problem.

[Roland Alcock]

This is a sensible suggestion as my feeling was that there was insufficient electricity available. My flashers have dedicated earths but I have not physically investigated the stop/tail and separate number plate light earths apart from with a meter.

[John Cornforth]

Some time ago I fitted LED bulbs to the stop/tail and front sidelights on my 12v Ruby. Recently, as I drove into the darkened garage, I noticed that the front side lights were coming on as I braked. Eventually found that the corncob type LED tail/stop bulbs were responsible.
On investigating I found that all of the individual |LEDs in the bulbs come on for both tail and stop function - but in tail lamp mode they are all dimmer.
There seems to be some kind of internal connection between the tail and stop pips which is allowing brake lamp voltage back out onto the side lamp circuits.
I cannot detect a resistance but suspect maybe a zener diode with poor reverse resistance..I put back the the old incandescent bulbs and all's well again.
I wondered if anyone else has come across this  - or has any other theories.

I had a problem with Stop/Tail LED bulbs from a well known supplier.  I discovered that the stop and tail pips supply only ONE set of internal LEDs via two different series resistors, to achieve different current drives for the two different levels of brightness.  In my car's setup, I found this rather simple arrangement caused interaction between the brakes and other parts of the sidelight circuit due to current flowing back out of the bulbs ("back feeding").  After a lot of time wasted working out what the problem was, I had to resort to putting in series diodes (1N4001's) in both sides of both LED bulbs to prevent the back feeding.  The diodes were hidden in the wiring with the aid of black heat shrink tubing.