Regen Braking & Rear Brake Lights

[old fisherman]

Just a general question. I use regen 3 a lot, and therefore very rarely use the brake pedal. Now I don't have eyes in the back of my head, so never know if my brake lights come on (if ever).

Does anyone know if they come on automatically ? Just asking, not very important to know.

Many thanks

 

[gary333]

Yes, they come on when regen is c.7 or above on the regen dial.

Some EV's are very annoying to follow if you do a lot of miles like me with the MG4 being particularly annoying as they are forever "braking", when not really braking the driver has just taken foot off accelerator a little too far.

 

[webhiker]

When regen/deceleration is above a certain level, defined by law, the brake lights come on.
That's what I've been told (I too do not have eyes in the back )

 

[MG Clive]

Some EV's are very annoying to follow if you do a lot of miles like me with the MG4 being particularly annoying as they are forever "braking", when not really braking the driver has just taken foot off accelerator a little too far.

I've learned to not take my foot completely off the accelerator if I don't want my brake lights to come on, but I do take my foot completely off the accelerator if I want them to come on.

 

[old fisherman]

Thanks for the quick response guys. Makes sense now, when some drivers in front of me "keep braking for no good reason" I'll be a little bit more understanding.

 

[siteguru]

The requirement is for the brake light to come on when the rate of deceleration exceeds 1.3m/s2. In the MG4 this is around the 7 or 8% regen mark. Regen levels 2 and 3 will make the brake light come on (provided that the battery isn't full, as will Regen A, usually), but Regen 1 will not as that tends to give a maximum regen of about 5%.

 

[Alb]

It's driven by a formula:

Post in thread 'Regeneration brake lights'

Nov 25, 2021

Deceleration ≤ 0.7 m/s2: The signal shall not be generated
Deceleration between > 0.7 m/s2 and ≤ 1.3 m/s2: The signal may be generated
Deceleration > 1.3 m/s2: The signal shall be generated

• Alb

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[ReintjeWA]

Can’t belief you didn’t take the chance to show off your nifty light setup @MG Clive

Thread 'Warning light added to show when the brake lights are on.'

Sep 2, 2025

Why? you may ask, well there has been so much discussion about when, and under what circumstances the brake lights come on, so I wired a small light into the brake lights to check for myself.

I found this so useful that I've now made it a permanent feature in my car, I just glance in my rear view mirror when braking, decelerating, or just lifting my foot of the accelerator, and I see the red led in my mirror.

This is the position of the light.


So I can tell you that the brake lights come on when:
You apply the foot brake (obviously).
You apply the EPB while moving.
When...

• MG Clive
• mg4 mg4 xpower
• Replies: 40
• Forum: MG4 XPOWER EV Forum

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[Everest]

I too do not have eyes in the back

@MGClive has

Warning light added to show when the brake lights are on.

Edited to add: Oops! too slow here

 

[MG Clive]

Can’t belief you didn’t take the chance to show off your nifty light setup @MG Clive

I know mate, I need to do a video of my brake light mod in operation.

 

[Everest]

I know mate, I need to do a video of my brake light mod in operation.

And @siteguru should do a commentary for that, complete with an inset power-point presentation, Chris Whitty style, to explain the deceleration forces and the rules when it lights up and doesn't Then post that as a sticky for the next 10 times the same question is raised