Separate Brake Light From Turn Signal

[Diver300]

Where is this third (center) brake light?
Is it not on the trailer that you are trying to light?

It's rare to have centre brake lights as standard on American trailers, because there is usually nothing to supply them from.

As I understood it, ThomsCircuit has bolted one on and is now trying to find how to supply it.

 

[Diver300]

Note: The third brake light has two sets of leds. It was designed as a marker light & brake light. I chose to connect the two together sets so it functions as a brake light only.

In the UK, it's common to have three brake lights on vehicles and trailers, so a left one, a right one and a centre, high-level one. However, trailers in the UK are allowed to have two high-level brake lights, because high up in the middle of the trailer may not exist, making fitting a central brake light there difficult.

Have you thought of adding two high level red lights, one each side, and just wiring each one in parallel with the existing stop/turn signal? That would give you a high-level brake light on one side or the other, unless the hazard lights are on.

 

[Diver300]

You could be lazy and do what is done on the Conch Tour Train.
On this:-

https://flic.kr/p/jzbeSm

the centre brake light just came on when either side stop/tail light came on. That meant that the centre light flashed when either turn signal was working, unless braking when it came on steadily whether a turn signal was on or not.
You could use two diodes or a relay to do that.

 

[ThomsCircuit]

The brake does not cancel the blinking.

Man, I really thought it did. It was the only way this would work but you are correct. I will ask the original poster if his conditions are the same.

 

[ThomsCircuit]

Where is this third (center) brake light?
Is it not on the trailer that you are trying to light?

yes. it is on the trailer. I just tested my trailer and you are correct. This is why I confirm everything I find with you guys.

 

[ThomsCircuit]

It's rare to have centre brake lights as standard on American trailers, because there is usually nothing to supply them from.

As I understood it, ThomsCircuit has bolted one on and is now trying to find how to supply it.

yes, it is rare and I have not connected or attached anything yet. I want to work out the circuit first. There must be some way. I will keep looking. Can't believe that guys relay circuit did not work. I'm still waiting on his explanation.

 

[ThomsCircuit]

the centre brake light just came on when either side stop/tail light came on. That meant that the centre light flashed when either turn signal was working, unless braking when it came on steadily whether a turn signal was on or not.
You could use two diodes or a relay to do that.

That is too easy. I would rather the third light not flash unless the hazards are on. Post 16 seems to be the best solution so far.

 

[ThomsCircuit]

Guess what my Tundra has!
"Built for towing, the Toyota Tundra is available with an Integrated Trailer Brake Controller."
I just access the on-board screen to activate it.

 

[Diver300]

Guess what my Tundra has!
"Built for towing, the Toyota Tundra is available with an Integrated Trailer Brake Controller."
I just access the on-board screen to activate it.
View attachment 145832

It's possible that it will just work and illuminate the light. However the car will alter the mark-space ratio to make the braking proportional to the deceleration.

It is possible that a relay operated by the brake wire would give more consistent results.

Also, check it stays on when stationary on the flat. The brakes my be deenergized in that state.

Otherwise, find the brake controller connector and it probably has the brake signal and the blue wire. Leave the brake controller disconnected, and join the brake signal to the blue wire in its place.

 

[crutschow]

It's possible that it will just work and illuminate the light. However the car will alter the mark-space ratio to make the braking proportional to the deceleration.

Just add a transistor with a RC filter to detect the trailer brake signal and drive the center brake light.
That will make the light intensity independent of the trailer brake signal amplitude (duty-cycle).

 

[ThomsCircuit]

Just add a transistor with a RC filter

like this? I found it on line. I apologize but I lack knowledge here. Could you help me finish this circuit?

 

[ThomsCircuit]

It's possible that it will just work and illuminate the light. However the car will alter the mark-space ratio to make the braking proportional to the deceleration.

I found a circuit using a few relays and diodes. Could you explain the logic behind this?

 

[crutschow]

I found it on line. I apologies but I lack knowledge here. Could you help me finish this circuit?

Something more like this below:
It detects the trailer brake signal which turns on the two transistors and energizes the brake light.

 

[Diver300]

I found a circuit using a few relays and diodes. Could you explain the logic behind this?
View attachment 145844

I wrote some rubbish just now so this is the edit.

That circuit should work, but you do need three relays, one of which is double pole. You could use two single-pole relays in place of relay 2.

What happens is that the relay 3 will energise when both turn signals are on, but will it will stay on if either turn signal is on, so it will only turn off when braking stops and both lights turn off.

When relay 3 is on, either turn signal being on will illuminate the brake light and will keep relay 3 turned on.

The brake light will flash in time with the indicators if hazard lights are on.

 

[ThomsCircuit]

What happens is that the relay 3 will energise when both turn signals are on, but will it will stay on if either turn signal is on, so it will only turn off when braking stops and both lights turn off.

When relay 3 is on, either turn signal being on will illuminate the brake light and will keep relay 3 turned on.

So as it is, with the dbl poll, it will work but if one of the turn signals is on when the brakes are applied the third light will remain on, steady, until the the turn signal is switched off even if the brake pedal is released.

 

[ThomsCircuit]

until the the turn signal is switched off even if the brake pedal is released.

...but only until the turn signal lamps on-off cycle changes state to "off". So even if the turn signal switch is engaged the relay should unlatch because the brake pedal was released changing one lamps state to off (open) and the other will be in the process of changing states from on to off thus an (open) state which would satisfy the circuit to reset.
Am I right? I think I'm right.

 

[ThomsCircuit]

Something more like this below:
It detects the trailer brake signal which turns on the two transistors and energizes the brake light.

Very nice. Thank you. Gota get a hold of an IRF7205. Could I use the IRF720?

 

[Diver300]

...but only until the turn signal lamps on-off cycle changes state to "off". So even if the turn signal switch is engaged the relay should unlatch because the brake pedal was released changing one lamps state to off (open) and the other will be in the process of changing states from on to off thus an (open) state which would satisfy the circuit to reset.
Am I right? I think I'm right.

That is correct. The brake light will stay on until both the lights are off. An indicator could stay on for up to an extra half second, so the centre brake could be late to turn off by that amount.

Similarly if the indicator is flashing, but in its "off" phase when the brake light turns on, only the other light will come on so the centre brake light could be slow to turn on by up to half a second.

 

[crutschow]

Very nice. Thank you. Gota get a hold of an IRF7205. Could I use the IRF720?

No.
That's an N-Channel MOSFET and the circuit needs a P-Channel device.
Just about any will work will at least a 20V rating and an on-resistance low enough to carry the brake lamp current without dissipating more than 1 watt.

 

[ThomsCircuit]

That circuit should work, but you do need three relays, one of which is double pole. You could use two single-pole relays in place of relay 2.

The original author wrote this.

"As options, the 2-pole relay could be replaced by two single-pole relays (R2a and R2b). A single pole logic relay with two terminals common, only three external wires, (R1 and R2a) could be replaced by a transistor sinking input to ground (for those who can figure out how to connect a transistor)."