Trailer light issues

[timhowarduk]

Hi
Ok, I admit this is nothing to do with a caravan....but the concept is the same.
I just changed the lights on my little box trailer for LED units. The problem is simple, it all works until I connect the brake wire (red). The lights seem to be designed to use the same LED's for running and brakes. The only instructions say:
Connection instructions:
Black: Negative
Green: License plate light
Blue：Running Light (Red)
Red: Brake Light (Brighter Red)
Yellow: Turn Signal Light (Amber)
Blue&Red Connect together
Now, as I want license plate light to be on with the running lights, I actually connected Green and Blue together on each side and connected them to the two tail light wires from the incoming cable. The incoming cable is wired using standard colours, so Brown and Black are the tail lights and Red is the brake lights.
In particular I can't fathom how the instruction "Blue and Red Connect together" works in practise - as I can't work out what I would connect them to on the car side. Every option seems flawed.
I'm feeling light I must be missing something obvious,and it's not making sense!
Here is a link to the lights in question: ebay item
Right now I have turn signals, running lights, but no brake lights. If I connect red to the brake light feeds the running lights and number plate lights go out.
Thanks for any pointers!

 

[timhowarduk]

I had a cup of tea. Maybe an idea. If the running and brake lights are the same LEDs with some internal witchcraft to make them brighter when braking, and the brake light wire from the car is at 0v (as opposed to floating), and I connect them up, it would cause the other lights to go out.
So is this problem because I don't have a split bypass relay the car side, and everything I have towed to date has had separate brake and running bulbs hence I've never encountered this issue? If I added a split bypass relay, would the brake wire be 0v or floating? Thanks!

 

[ProfJohnL]

I have looked at the ebay item, and like you the wiring instructions do not seem to make sense.

My suspicion is these are a Chinese import product, and something has been lost in the translation. Contact the supplier.

 

[Dustydog]

Tim,
Agree fully with the Prof.
Just check the integrity of your earth connections all the way through including the car.

 

[timhowarduk]

Thank you both, yes, definitely Chinese import item, I've contacted seller.
It's a sealed unit, with one Negative wire coming out of it, wired straight through to the car. I'll check but I'd imagine that nothing would work if it was an earth issue.
My speculation would be:
1) it is supposed to tell you to join the running lights and license plate light wires together, as you don't have separate two feeds for them anyway
2) I think this thing can only work if brake wire is floating or 12v and never 0v, as it seems to connect to the same LEDs through more resistors to brighten them up for braking. I suspect that if cars have a bypass relay this would be the case. In my case (no relay) the brake wire will be at 0v via the brake bulbs in the car. If anyone happens to know whether a bypass relay in the car would indeed leave the brake wire floating I'd be interested to know. I might try bunging a dioide in that wire to prove the point.
thanks all
Tim

 

[ProfJohnL]

Thank you both, yes, definitely Chinese import item, I've contacted seller.
It's a sealed unit, with one Negative wire coming out of it, wired straight through to the car. I'll check but I'd imagine that nothing would work if it was an earth issue.
My speculation would be:
1) it is supposed to tell you to join the running lights and license plate light wires together, as you don't have separate two feeds for them anyway
2) I think this thing can only work if brake wire is floating or 12v and never 0v, as it seems to connect to the same LEDs through more resistors to brighten them up for braking. I suspect that if cars have a bypass relay this would be the case. In my case (no relay) the brake wire will be at 0v via the brake bulbs in the car. If anyone happens to know whether a bypass relay in the car would indeed leave the brake wire floating I'd be interested to know. I might try bunging a dioide in that wire to prove the point.
thanks all
Tim

I understand your thinking now. Your considering the probability the same red leds are used for both running and brake lights duties, but the running lights have some form of current limiting on the blue wire which reduced the intensity of the red pack. The full intensity will only be produced when 12V is fed to the Red wire which electrically short circuits the current limiter, and provide full current to the red led's. consequently if the red wire is loaded by filament bulbs (the brake lights) they will provide a low resistance path for the led current and prevent the LED from illuminating.

A diode in series with the red wire may correct the problem, But I have a niggling suspicion the UK construction and use regulations calls for separate illumination for side and brake light functions, in which case the led pack would not comply. as teh same light source is being used for both functions. In years gone past we used to have dual filament bulbs to get round this requirement.

 

[philip_stevens]

Tim, if you can get the supplier to send you the instructions in either Mandarin or Cantonese, and copy them to me, my Chinese daughter-in-law can do a "proper" translation. This is what she does for a living.

If they can be sent to you, let me know and I will PM my email address.