Regarding regen and brake ligth

I was asked earlier about I could create something so that the brake light will come on when regenerating.
I have now seen on it and I see that the Sevcon Controller is already configured to activate the brake lights when regenerating. you only need to connect a wire to pin 11 of the 35 pin connector to the controller. this wire should then go to one relay that provides power to the brake light and it’s done :slight_smile:
to add a wire to the 35 pin connector you need one crimp socket as this,

And a relay like this

I have not tested this but it should work :-))

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@kennethnilsen69: Thanks! The order is placed. The seller is rather slow in sending the socket [Estimated delivery: Thu, Apr. 28–Thu, May. 12], but when the socket arrives I get on with the mod.


@shthpnz yes that’s the one

Here you have an old youtube video I made a long time ago that shows how to add a Pin to 35 pin connector.
just remember that you should add to Pin 11 and not 18 as shows in this video

Thanks for the video.
Please point me out which one is #11

if you look at the connector as it is in the picture so are the Pinout like this



Hi! @shthpnz ! Were you able to make this? Did it work?

@cosimo_terzani: Yes I did.
The video of Kenneth was very helpful in

  • how to unconnect the 35 pin connector.
  • how to open the connector 5mm and
  • how long the new wire has to be stripped of its insulation (approx the lenght of the crimp socket), and soldered over that lenght and completed with a shrink thing.

Take good notice that the crimp socket has to be smooth on the part where the wire is crimped in. The whole connector (and more) has to go through a small hole on the back side of the 35 pin connector.

The wire bundle of the disconnected 35 pin connector doesn’t give you a lot of handling space in/under the motor compartiment. So it is a challenge to get the wire-with-crimp socket in slot #11. Patience is your friend.

More later.

Thank you @shthpnz ! This part is now very clear to me! So at the end this solution worked for you?
Sorry to bother you but how does the rest of wiring works from the 35 pin connector to the stop light?

Hello @cosimo_terzani. When you asked me if I was able to make the brake light mod it was on the second day of my first free days in a long time. But you ignited the realisation of it :slight_smile:

Yesterday I made the connection in the 35 pin connector.

Kenneth suggested that pin #11 gives a 12V signal when regenerating. Then that signal can alert a relay which switches the brake lamp. (Edit: I was wrong with pin 11 giving 12V. See the remark of Kenneth below)

The wire to the brake lamp, GND and the 12V all can be accessed under the dash. From the switch on the brake pedal run four wires: GND; 12V; a fault signal and the brake light wire.

So the only job is to bring the wire from pin #11 to the dashboard and he rest can be found on the wires to the brake switch.

Bringing wire #11 towards the front of the car is rather easy when you remove most of the plastic parts around the left door and the long black plastic shield on the left underside.

Pull the wire horizontally through the left underside, next to the fat plastic cable bundle;
on the front side of that tunnel go to the inside towards the floor cavity under the lid in the footwell in front of the seat (where the handbrake cables split)

You see that on the left side of the footwell there is a vertical tunnel. Pull the wire through that tunnel from the front outside under the left headlight upwards, let it enter into the dashboard space from under the left square under the left headlamp and you have the wire where you want it.

I use these rods to do the job.

So far so good. Before realising the relay connections I checked the behavior of wire #11. It only gives some faint voltage, always below 1 V, even when regenerating at 500. It does not discriminate between accelleration and regeneration. The faint voltage drops when using the brake.

So I run into a problem and will not commence to connect the relay at this moment. Perhaps @kennethnilsen69 can help me out?

Hi @shthpnz why you failed to measure more than about 1 volt is because Pin 11 outputs GND and not +12 volts when it becomes active. you must connect pin 11 to GND on the relay and bring +12volt from the battery. Run now test to see if the relay is active when you regenerate.

PIN 11 outputs + volts when it is not active and is probably not more than about 1volt that you have measured

Take a look in Sevcon manual on page 40 so it is explained there

@kennethnilsen69 Thanks for the explanation! I was wrong in my assumption and will change that above.

Tomorrow I will make those adjustments. And keep you all updated.


I connected pin #11 to 86
connected +12v to 85
connected +12v to 30
laid voltmeter + to 87
laid voltmeter - to GND

What has to happen is that when the Twizy is regenerating pin #11 connects to GND, giving a current from 85 to 86, which activates the connection between 30 and 87.

What happens: NOTHING when the Twizy regenerates, but when applying the brake WHAM the voltmeter reacts! 14V. You clearly hear the relais make its shift. Even when the car is not moving.

So pin #11 goes to GND when the brake switch is applied, and on nothing else.

And to be sure I used pin hole #11 on the 35 pin connector (the black wire) :slight_smile:

How do we get from here?

It may then seem that the ECU is only set up to activate PIN 11 when you step on the brake. I will look at it when I get home from my vacation.

Thanks for the answer. I didn’t realize you were on vacation. Please enjoy the rest of your holidays :yum: We hear from you later.

Did you get it sorted in the end? I thinking about doing the same.

I didn’t even know there was a solution for this.

My Tesla brings the light on based on the severity of lift off of the brake pedal, could be G related, but works nicely and doesn’t scare people behind when coasting to the lights.

Sorry not having updated you all.

I closed the project. Removed the wires and the solenoid. It is a pity.

I believe an easier and more successful attack route will be the use of a gravity / acceleration / decelleration switch. When gravity changes due to decelleration the switch does its work by letting current go to the brakelights. That feature will dramatically enhance the safety of us Twizy drivers in traffic.

Those sensors with switch are miniature, cost effective and rather easy to install.

I will not continue this project, who will?

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