LED tail/stop bulb connundrum

[squeak]

I had similar troubles as John Cornforth with my installation of 6v LED stop/tail light board to the ruby pork pie. He has explained it much better than I could have, but the solution of inserting a diode to stop feeback  was simple and completely successful.  cheers  Russell

[Roger J]

I've been out this eve so just read thru the thread. John C seems to be reporting an almost identical problem.
But I will address the suggestions of bad earths first. My checks started with that assumption although the symptoms didn't seem to fit.
in fact the front sidelights are well earthed at the front of the car and I couldn't see how and earth fault could do anything other than make them fail to come on properly, or at all, They share an earth with the 36W headlights which work OK.
I only have the two examples of the stop/tail LEDs which were cheap Chinese "corncob" types off eBay. It's quite possible that all the advertised ones are not all the same - and some types I see illustrated there have two quite separate LED element is the "BulB" These would probably not be affected.
Tomorrow I will test my examples more thoroughly and satisfy myself that current is back-feeding from the other (tail) pip
It's too late tonight to see if my particular examples can be made serviceable with the inclusion of a diode(s). I'd need to get my head around exactly where to insert it after satisfying myself what's going on..
meanwhile it's good to know that this effect has been seen elsewhere..Roger

[Roger J]

Ok...proper testing done..These results may only apply to the examples of the corn-cob style stop/tail bulbsI have (bought over a year ago) and may not be the same as others - but obviously similar to the ones John C has. In these bulbs all of the leds light up in either mode but with different brightness.
Out of interest the tail light mode consume about 0.1 amps each and the stop light mode about 0.25 amps.
When the "stop light" comes on e a voltage appears on the tail light pip about 2 diode drops below the battery voltage.
This "source" has a source impedance of about 33 ohms - ie a short circuit current of about 0.3 amps is available.
Enough to light other led lamps on the tail light group at slightly reduced brightness..May even make an incandescent front side light glow a bit (I didn't try)
No back voltage was output from the brakes light pip when the tail lights were on.
So the effect could be cured ( as John said) by including a small diode (IN4001) in the feed to the "tail lamp" of each"bulb".
Something to be aware of if you buy corn-cob style stop/tail LEDs..Roger

[leaf200]

Hi all,

I have the same issue. It is not caused by bad earth it is caused by the fact the stop tail lamp uses the same LEDs but has two different resistors fitted one stop and one tail. on activation of the brake 12V is applied to the bottom of the Stop Resistor which as the effect of feeding back down the tail connection via the two resistors in series. as both tail and side are connected to the same switch panel terminal it dimly lights the side lights. a diode to stop the feedback will fix the issue

Thanks

[GK5268]

I had the same problem several years ago, and spent some time sorting it out, including returning the original units back to the supplier, who sent replacements that were supposed to have cured the problem, but didn't!

The problem is within the light boards themselves, the brake & tail light circuits leak current, because of the low requirements for the LED to work any leakage will illuminate or switch off other lights - applying the brakes gave rise to the side lights coming on (if LEDs are fitted, normal bulbs don't have the problem as there is insufficient current for them to illuminate).

The other issue was that with the ignition turned off, and the side lights turned on, the brake pedal applied (become live with the ignition on, but with ignition off, the lights were "dead"), the tail lights would dim down, leakage from the light boards causing the current to reduce and causing the dimming. 

It was not an earth issue on my car (it was all brand new wiring), but an internal wiring problem with the light boards.

However, it was all fixable, I inserted a diode into each connection to the light board wires so that the current could only flow in one direction only (previously, it was free to go both ways).

This has solved the problems and everything works now as they should.

The diodes cost pennies and I just soldered these into the respective wires and put heat shrink over & re-connected, simple to do!

[Robert Leigh]

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.

I found that buying cheap LED lamps from Ebay means that you get what you pay for, and back feed problems can arise. After speaking to Peter Jury at Classic Dynamo and Regulator Conversions I bought (at a higher price) some of his which apparently have diodes in their construction to prevent the back feeds, and my problem was solved. There may be other suppliers of lamps who do the same, but another good feature of the Classic Dynamo lamps is that they have colour emitting LEDs to suit the function you need, so that even with a broken rearlight cover you still have red lights at the back.