High Level LED Brake Light Problem

[Harveyzone]

Hi all,

So I swapped out my stop/tail bulbs for LEDs. A straight swap, and all ok.

But whilst I was at it I thought I would add a high level 3rd brake light, and that is where the problems started.

I simply connected the +/- wires of the 3rd light to the +/- of the brake light connector at the rear bulb holder. So far so good. All working correctly. However, as soon as I turn on my lights the 3rd light comes on and stay on continually. Rear lights still work correctly. When I press the brake pedal the 3rd light gets a little brighter. 

When the tail lights are on I seem to get around 9v on the brake lights which goes up to around 11v when the brakes are applied. It is at 0v/11v when the tails lights are off. There is some sort of bleed/short between the tail and stop lights that is not enough to light the rear bulbs, but is enough to light the 3rd light that I have added.(It's a Spitfire 1500, if that makes a diference).

Is there someone who knows more about electricity that I do that can tell me how to fix this?

Many thanks,

Tom.

[Howard]

I have just looked at a 1500 wiring diagram and it shows that there are separate rear and brake light bulbs. Can you please confirm this is correct?

My immediate suspicion is that there is a poor earth connection which could cause symptoms like you are experiencing. I suggest running a temporary earth wire from the rear light lampholder to the battery negative terminal & the measure the voltage across the brake light with the rear light turned on - it should be 0v!

Cheers

Howard

[Harveyzone]

Hi Howard,

My first thought was earth - it always is with light problems!

On a 1500 they are a single bulb for stop tail - two filaments traditionally, but just dim/bright on an LED. The one bulb holder has an extra earth connector on it which runs to the body. The other one doesn't - it relies on the clips to earth against the cluster.

I am pretty sure that the earths are all good, but just to be sure I have run a wire back to the battery as you suggest. I get 0/12v off/on for the tail lights. I get 0/12v off/on for the brake lights when the tail lights are off. AS soon as I put the tails light son I get 8/12v for the off/on for the brake lights (!)

I have tried two different sets of bulbs - the first set were cheapy ebay ones which I couldn't get to work, the second set are more expensive ones from a reputable dealer, which were recommended by several people on various forums, which display the same symptoms. I have all but eliminated the bulbs as the problem (unless I am very unlucky!). 

Tom.

Edited June 2, 2023 by Harveyzone

[Howard]

Tom,

Somewhere there is a bad circuit that is back feeding into the brake light circuit, Can you post photos showing the rear wiring of both bulb holder so I can give you some more pointers about how to test and check for the fault.

Alternatively if you are on WhatApp I will PM you my phone number so we can have a video chat and look at the problem .

Cheers

Howard

[JohnD]

Triumph just earthed the bulb holders to the housing, and assumed that made enough contact with the bodywork to be good enough.  But after fifty years or so, it don't!  Usually because of corrosion between the pot-metal housing and the body.

Take a jumper lead, crocodiles both ends, and earth the light housings until you get correct function.   Then arrange a permanent earth in the jumpers place, to the adjacent body, remembering that you might want to take off the housing at some future time!

John

[Dannyb]

I had a strange problem when I added stop/tail lights to my Spit 1500. I had already put separate  earth wires in some years ago so I knew the earth was good. It turned out that inside the bulb holder there a small earth clip that needed bending to make better contact with the side of the bulb. The led bulb barrels were very slightly smaller than the old.

Danny

[Harveyzone]

Hi all,

Apologies all - events have transpired against me and I have only just had a chance to look at this again after two weeks of other priorities.

I checked out all the earths again, and all looked good, so I decided to take the car and even the bulb holders completely out of the equation and just connected the bulb directly to the battery. Outside straight to earth, and 12v across one connector then the other - I get a bright light from one side, and a dimmer light on the other - one for stop and one for tail, as it should be.

Now, if I take some volt readings, I get the 12v on the side connected to the bulb connector, as expected, but I get c10v coming across the bulb and the other connector, when nothing is connected to it. This 10v is obviously what is going back up the brake light circuit when the lights are on and is lighting the high level light. If I swap t the other connector I get exactly the same, but a bright/dimmer light (depending on the side).

So I am getting 10v leaking across the LED bulbs.

I have tried this on all six LED bulbs of two different designs, from two different sources, (one, a no-name ebay seller, and one, Badboy Classics, that were recommended to me) and they all do the same.

Is this a 'feature' of all combined stop/tail LEDs, and if so, how do you deal with it?

I know that you often need ballast resistance connected in parallel for LED indicators lamps, but I understand that this is due to bleed through the dash board light and shouldn't(?) be an issue for stop/tail circuits. 

Would adding resistance to one/both circuits make a difference, and if so, where?

Has anybody else see this problem? How was it resolved?

Is there anyone who has successfully replaced their stop tail bulbs with LEDs that could do a quick voltage measurement across the connectors when only one of them has power to see if they get similar bleed?

Apologies - my knowledge of electronics is pretty basic.

Many thanks,

Tom

Edited June 18, 2023 by Harveyzone
Additional question.

[Harveyzone]

And an additional thing that I have just noticed (hadn't noticed this before as I had been concentrating on the rear light clusters), but which makes absolute sense now that I know what the cause of the problem is, is that when I apply the breaks, the 10v bleed (in the opposite direction), causes the number plate and front side lights to light up.

[drofgum]

Harveyzone,

I think you are going to need to insert a diode into each supply wire to those LED bulbs. That way the applied power will not be able to go back out on the other line.

 Regards,

Paul

[Harveyzone]

9 hours ago, drofgum said:

 think you are going to need to insert a diode into each supply wire to those LED bulbs. That way the applied power will not be able to go back out on the other line.

Thanks Paul - That sounds like a sensible approach that I hadn't though of. I don't think I have any, but I will see if I can get hold of some and try it.

Shouldn't have to mess about like that for bulbs that are advertised as a straight swap for conventional bulbs. 🙁

[DVD3500]

What about wiring it into the the cable coming from the brake switch?

 

[Kevin R]

As an aside but related problem, I replaced the four high wattage halogen bulbs in our cooker hood with the lumen output equivalent LEDs and they did not work.

By chance I put one of the halogens back in and the remaining three LEDs worked fine so presume it is fulfilling the ballast resistor role.  Some sort of improvement (75% ish) but not a total success.  ☹️ 

[Harveyzone]

Hi all,

By way of a quick update, I got hold of some diodes, and soldered them into some fuse holders with the springs removed, and a male/female spade clip on each end. They now just slot neatly into the existing circuit, and are easy to remove if necessary.

This seems to have solved the problems! 🥳

One set of bulbs refused to work properly, which I think is due to the fact that I am only getting about 10.5v at the bulb on the brake lights circuit (they seem to work with 12v, but not with 10.5v) but the other sets worked as advertised, so obviously have different tolerances, but overall I am happy🙂.

Now on to the next problems, whatever they are...

Thanks all,

Tom.

Edited June 27, 2023 by Harveyzone

[drofgum]

Tom,

Have you tried the non-functioning bulbs in the sockets where other bulbs worked? That will show whether the bulbs are the reason or if there is some problem with the sockets.

Regards,

Paul

[Harveyzone]

On 28/06/2023 at 15:01, drofgum said:

Tom,

Have you tried the non-functioning bulbs in the sockets where other bulbs worked? That will show whether the bulbs are the reason or if there is some problem with the sockets.

Regards,

Paul

Hi Paul,

Yes, I have directly swapped the bulbs around and tried them all in each others sockets.

I have actually bought a couple of news cheapy bulbs off ebay that were advertised as 10-30v rather than the 12v that are generally stated, (just out of curiosity), and they are far, far better. Much brighter than the previous working bulbs, and much greater differentiation between between the tail lights, and when the brakes are applied. I am fairly sure that the old wiring is losing some power and that some bulbs are better able to cope than others.

Not all LED bulbs, even from reputable sellers, are equal!

Tom.