Separate Brake Light From Turn Signal

[ThomsCircuit]

I have seen devices, designed for trailer output, that can separate the turn light from the brake light. How is this accomplished? I would like to reproduce this.

 

[ThomsCircuit]

Found This. I understand most of this. The input is on the right, output on the left. I have all but the darlington 2N6388. Could I use a TIP122 & 142? It's what I have.

Thank you in advance.
T.B.

 

[Diver300]

As you have probably realised, the adaptor can't simply use the current state of the lights. For example, when the left light is on and the right light is off, that could be either turning left and not braking or turning right and braking.

The adaptor has to use whether the lights have changed state recently or not. If a light is flashing as a turn signal, it will always have changed state recently. You then get the following rules:-

0 Left on, not changed, Right on, not changed - brake only
1 Left on, not changed, Right on, changed - brake and right indicator in on phase
2 Left on, not changed, Right off, not changed - unknown state
3 Left on, not changed, Right off, changed - brake and right indicator in off phase
4 Left on, changed, Right on, not changed - brake and left indicator in on phase
5 Left on, changed, Right on, changed - both indicators (hazard lights) in on phase
6 Left on, changed, Right off, not changed - left indicator only in on phase
7 Left on, changed, Right off, changed - left indicator only in on phase
8 Left off, not changed, Right on, not changed - unknown state
9 Left off, not changed, Right on, changed - right indicator only in on phase
10 Left off, not changed, Right off, not changed - all off
11 Left off, not changed, Right off, changed - all off
12 Left off, changed, Right on, not changed - brake and left indicator in off phase
13 Left off, changed, Right on, changed - right indicator only in on phase
14 Left off, changed, Right off, not changed - all off
15 Left off, changed, Right off, changed - all off

So off will just be state 11
Braking only will be state 0
Left indicating only will alternate between states 6 and 14
Right indicating only will alternate between states 9 and 11
Left indicating and braking will alternate between states 4 and 12
Right indicating and braking will alternate between states 1 and 3
Hazard lights will alternate between states 5 and 15

The circuit has to remember if a light has changed recently, and then use rules like that to decide which outputs to drive.

The actual adaptor is probably more sophisticated than that because when braking starts, the state will go from 11 to 5 initially, and then to 0, so the indicators would flash once and the brake light would be slow to light. Maybe when both turn on at the same time, that is a separate state. Maybe a light is only assumed to have changed when it turned off recently.

Whatever the rules are in detail, the system never has to light anything when all the lights are off, so the adaptor can always get power from one or other of the lights.

 

[Diver300]

View attachment 145809

Found This. I understand most of this. The input is on the right, output on the left. I have all but the darlington 2N6388. Could I use a TIP122 & 142? It's what I have.

Thank you in advance.
T.B.

That circuit is for going the other way, for a European car with separate brake lights and direction indicators, towing an American trailer with combined stop/turns signals.

(The stop / turns signals in that diagram are confusingly called right side and left side. On a European towing socket there are two connections called right side and left side. They are the position / marker / tail / number plate lights, which are split left and right so that one side only can be lit when the car is parked. On American and Australasian towing systems, there is a single connection for all the position / marker / tail / number plate lights)

 

[ThomsCircuit]

The actual adaptor is probably more sophisticated than that because when braking starts, the state will go from 11 to 5 initially, and then to 0, so the indicators would flash once and the brake light would be slow to light. Maybe when both turn on at the same time, that is a separate state.

Thank you for listing all the possibilities. I will keep looking.

 

[ThomsCircuit]

How about this? It would work only when the brake is pressed and it would also flash when hazards are engaged.

 

[Diver300]

How about this? It would work only when the brake is pressed and it would also flash when hazards are engaged.

View attachment 145810

I don't think that would work.

The relays with the 87A terminal will disconnect 87A from 30 when power is applied across 86 and 85.

So you would get:-

Both off -> brake light off
Right on -> brake light on
Left on -> brake light off
Left and right -> brake light off

So when braking, that would give nothing.
When indicating right, the brake light would flash like the right indicator
when indicating left, that would give nothing
when braking and indicating right, that would give nothing
when braking and indicating left, the brake light would flash on when the left indicator is on and vice-versa.

As I said in the first paragraphs of post #3, any system needs to know what happened in the past, When one light only is on, the vehicle could be braking + indicating or it could be indicating on the other side.

It's a job for a microcontroller. I would be very surprised if the the relay from Curt doesn't contain one.

 

[crutschow]

Below is the LTspice sim of an XOR power gate using MOSFETs that combines the separate brake and turn light signals from the vehicle into the combined Turn & Brake signals to the trailer:

You will need two circuits, one each for the left and right bulbs.

The P-MOSFETs can be just about any 20V rated that have ≤0.04Ω on-resistance.

 

[Diver300]

The OP is looking for a circuit to do the opposite. He wants something to extract a brake signal from the left and right combined stop/turn signals.

 

[ThomsCircuit]

I don't think that would work.

The relays with the 87A terminal will disconnect 87A from 30 when power is applied across 86 and 85.

Thats a shame. The fella that posted this said his did work. I did make one mistake. brake light goes to 87 not 87a.
I reached out to him for clarification but I do see you point.

 

[ThomsCircuit]

You will need two circuits, one each for the left and right bulbs.

Thank you but i mistakenly thought the example I found in post 1 did what I needed. Diver300 is right I want to extract the brake light from the combined turn/brake light. What I posted does the opposite. Yours looks easier to read.

 

[crutschow]

I want to extract the brake light from the combined turn/brake light.

That's not what your trailer connector shows.
It has combined tail/brake signals to the trailer lights.

 

[ThomsCircuit]

That's not what your trailer connector shows.
It has combined tail/brake signals to the trailer lights.

Yes, the trailer output connector has a combined R-turn+Brake and L-turn+Brake. I want to add a third ONLY brake light. Can you help me with this?

 

[ThomsCircuit]

Why this works.
The brake "signal" over-rides the turn "signal".
If a turn signal is activated the relay will not engage because only one light is activated. If the brake pedal is pressed both lights are triggered and a steady light is displayed thus activating the relay. If either turn signal is activated while the brake pedal is pressed the brake pedal signal over-rides the turn signal request and the light remains steady. the only time the third brake light will flash is if the hazards are activated.

 

[crutschow]

The brake "signal" over-rides the turn "signal".

That connection does not make sense.
The only inputs are the Left Turn/Brake and the Right Turn/Brake.
So how does the brake light come on steady when the Right Turn/Brake (pin 30) is a steady "Brake" signal and the Left Turn/Brake (pin 86) is blinking.
(Relay connection diagram below):

 

[Diver300]

If your trailer does not have electric brakes, you could use the trailer brake wiring like this:-

Connect the trailer lights to the blue (trailer brakes) wires.

At the front of the car, under the steering column, find an unconnected connector with 4 wires. One of these will be blue, and will be the other end of the trailer brake wire.

In that connector the three other wires. One will be ground, one will be permanent power, and one will come on when you brake. Work out which is which and connect the one that comes on when you brake to the blue wire.

The handbook may have more details. Look for "trailer brake controller".

 

[ThomsCircuit]

So how does the brake light come on steady when the Right Turn/Brake (pin 30) is a steady "Brake" signal and the Left Turn/Brake (pin 86) is blinking.

That pattern combination cannot happen.
There are just 5 possible outputs
---------------------------------
0-Left & Right Off (default)
1-Left Blinking & Right Off (left turn)
2-Right Blinking & Left Off (right turn)
3-Both Left & Right Blinking (hazard light request)
4-Left & Right Steady (pedal pressed)
---------------------------------
The relay will only engage under conditions 3 or 4
If Left or Right is blinking & Brake pedal is pressed than both Left and Right will go steady. Brake pedal request over-rides turn signal requests thus changes the blinking light to a steady light.

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.

 

[ThomsCircuit]

If your trailer does not have electric brakes, you could use the trailer brake wiring like this:-

Connect the trailer lights to the blue (trailer brakes) wires.

At the front of the car, under the steering column, find an unconnected connector with 4 wires. One of these will be blue, and will be the other end of the trailer brake wire.

In that connector the three other wires. One will be ground, one will be permanent power, and one will come on when you brake. Work out which is which and connect the one that comes on when you brake to the blue wire.

The handbook may have more details. Look for "trailer brake controller".

Awesome Idea!

 

[crutschow]

There are just 5 possible outputs

No.
If one side is blinking and the brake is applied, then that side remains blinking and the other side goes on steady with the brake.
The brake does not cancel the blinking.

 

[crutschow]

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