Ignition Switch Contacts: Current Capacity?

Hello,

For years, I've been wondering why the brake lights on VAG vehicles are always on.
For example, someone might be waiting in a parking lot for their partner, and without thinking, they put their foot on the brake pedal, and suddenly the battery, even with the ignition off, is drained at about 6 amps (including the third brake light).

Now that we know that each discharge cycle reduces the battery's lifespan, I want to at least rewire the brake light power supply to the ignition switch.
(The X-relay would be even more interesting: then the brake lights would turn off when the accelerator is pressed, but this would create implausible brake switch signals, which could lead to confusing MSG error messages or a fail-safe mode.)
However, for that to be possible, the ignition switch contacts would still need to have sufficient electrical capacity.
I estimate that the potential maximum current draw on terminal 15, from sources such as reversing lights (4A), infotainment system power supply (2A), windshield washer pump (2A), WIV oil pump (2A), recirculation flap motor (1A), and activation currents for various control units, is approximately 12 amperes.

If I were to connect the brake lights, the maximum load would increase by about 50%, so it's not a negligible amount.
I would only consider using an additional relay as a last resort, when there are no other reasonable solutions.

-> Does anyone know what the typical current load rating is for the ignition switch contact 15?

Hi,

I'm not sure if such a modification is legal. I can imagine good reasons why the brake lights should work even without the ignition being turned on.

I don't quite understand the "problem"... when I have the engine off, I take my feet off all the pedals and use only the handbrake to prevent the car from rolling.

Best regards,

Jan.

In any case, the operating license and insurance coverage will be voided by such pointless modifications.

I installed a battery, so I can keep my foot on the brake all night, and the car still starts, which I tested by having the brake light switch stuck.

Best regards, Rüdi.

Rüdi wrote:

In any case, the operating license and insurance coverage will be voided by such nonsensical actions.

Why? Is it stipulated in the regulations that the brake light must also work without the ignition being on? If it's installed correctly, there's nothing against it. The German Road Traffic Act (STVZO) doesn't have a problem with the brake light only working with the ignition.

Aron wrote:

Is it stated in the BE (German vehicle registration document) that the brake light also works without the ignition being on?

If it is installed correctly, there is nothing against it; the STVZO (German Road Traffic Regulations) has no problem with the brake light only working with the ignition on. }
Even though it's off-topic compared to my question:

I completely agree, especially since the brake light on my older French cars only came on when the ignition key was turned.
"However, their headlights were completely dependent on the battery positive terminal (B+), and you could play full-blown Christmas carols on the horn: again, VAG is better in this regard, as they disable the low and high beams via an X-contact when starting the engine."

@Jan: What good reasons can you imagine for the brake light being powered from the B+ terminal?

Hi,

Quote:

@Jan: What good reasons can you imagine for the brake light being powered from the B+ terminal?

An improperly parked car rolls away without a key inside, someone steps on the brakes, and the car comes to a stop in the middle of the road - making it more visible from behind.

The car is stopped with its engine off at the end of a traffic jam (not exactly on the highway, where it would be better to use the hazard lights). The driver puts their foot on the brake to make the car more visible to the driver behind.

Towing: As long as you turn the key to the ignition once and then turn it off again, the steering wheel lock will not engage. You don't need to use the turn signals, as the hazard lights are already on, but the brake lights will come on without needing to turn on the headlights.

I didn't know that wouldn't work on French cars; I never really looked at that part closely, thanks to my sister. But you often see people leaving their headlights on in parking lots...

Best regards,

Jan.

ulf wrote:

Hello, For years, I've been wondering why the brake lights on VAG vehicles are always on.

Since 1990, it has been a European Union regulation that brake lights must function independently of the ignition key.
However, I don't understand how some manufacturers still manage to obtain approval for their vehicles, even though the brake lights turn off when the ignition is switched off.

Quote:

For example, someone might be waiting in a parking lot for their partner, and without thinking, they put their foot on the brake pedal, and suddenly the battery, even with the ignition off, is drained at approximately 6 amps (including the third brake light).

Actually, I wouldn't worry too much about the battery. The lights themselves don't last very long. Two years ago, I ruined two taillights at the alignment shop. There, the brakes get stuck, which causes the lights to burn out. After about an hour of work, the plastic had melted.

Quote:

... I estimate the activation current for various types of sensors to be in the range of approximately 12 amperes.

I hope that the decimal point is simply misplaced. 12A doesn't go through a traditional ignition switch anymore. Nowadays, it's managed by "Power Management Modules," which only require a few µA from the control unit.

Quote:

... -> Does anyone here know what the general current load rating is for the ignition switch contact 15?

S-Contact 500mA.
Terminal 15 can provide up to 10A of power, depending on the vehicle (and car radios should theoretically not be connected to it).

But to answer your question:
I hope you understand that the braking system and its signaling components are safety-critical components. Any modifications to these components will immediately invalidate the operating permit (ABE) and can have serious legal consequences. In some cases, even for non-professionals, this could potentially lead to imprisonment. Workshops are even required to specifically document and archive any work performed on these components.


But slowly, I believe that the electrical system of your Polo is so dilapidated that it's no longer worth undertaking such a conversion. Just get rid of the car.
Whether your battery lasts two days longer before it finally fails is likely of little importance .

Quote:

Since 1990, it has been a European Union regulation that brake lights must operate independently of the ignition key. However, I don't understand how some manufacturers still manage to obtain approval for their vehicles, even though the brake lights turn off when the ignition is switched off. Quote:

Hello!

Is this regulation still in effect?
If I remember correctly, some newer VW models (Golf Plus, Touran? I'm unfortunately not sure exactly which ones) no longer have the brake light connected to the constant positive terminal.

I was also quite surprised, as I've always preferred it when the brake light is connected to a constant power supply.

Bertil wrote:

Since 1990, it has been a European Union regulation that brake lights must function independently of the ignition key.

While I don't want to delve too deeply into this (OT), I can only read in the German Road Traffic Regulations (STVZO) that the electrical system must be designed to ensure safe operation, and that, for example, the brake lights on the left and right must be separately protected.

Aron wrote:

... "However, I can only read in the STVZO (German Road Traffic Regulations) that the electrical system must be designed to ensure its proper functioning." ...

The German Road Traffic Act (STVZO) does not cover all regulations regarding vehicle registration and roadworthiness.

Quote:

Is this regulation still in effect? If I remember correctly, some newer VW models (Golf Plus, Touran? I'm unfortunately not sure exactly which ones) no longer have the brake light connected to the constant positive terminal.

Yes, it is still valid (I double-checked to be sure).
However, it is possible that there are individual approvals. Some vehicles even have partial brake light activation via CAN bus!

However, I am also aware that the lighting sector is currently undergoing massive changes.
LED headlights (like those in the R are currently not permitted. The R8 has a special permit for these headlights. These lights are not expected to be approved for mass production until next year.

Bertil wrote:

... Quote: Is this regulation still in effect? ... Yes, it is still valid (I double-checked to be sure). ...

Command retracted...
In an addendum, it is actually permissible to not operate the brake lights via the "Dauerplus" (constant positive terminal). I had overlooked that.

Hi Bertil,

That would have surprised me too, because neither my father's W202 nor his current W203 does that. Your E-Class probably won't have the brake lights illuminate when the key is removed either...

My brake light on my Golf V only comes on when the ignition is on.

SGM

Bertil wrote:

Command retracted... In an addendum, it is actually permissible to not operate the brake lights via the constant power supply. I had overlooked that.

Ah, okay.
Do you happen to know if this regulation is available online for viewing?

*ggg* I don't think the battery will last significantly longer with such a modification. Besides, there's already a ready-made device that solves Ulf's problem: it's a long lever with a button on the front, usually located between the driver and passenger seat. You can use that and then relax your foot from the brake.

@Ulf: Don't you want to get into C167 assembly? There are really some beautiful things to explore there .

Best regards, Rainer.

ulf wrote:

... Do you happen to know if this regulation is available online for viewing?

Online, not at all. The KBA (German Federal Motor Transport Authority) already takes care of that. Even publicly available copies are severely punished. After all, they make a lot of money from it. Moreover, one shouldn't make it any easier for potential car manufacturers to build a car.

Rainer K. wrote:

I don't believe that the battery will last significantly longer with such a modification.

Dooooch .... definitely two to three days ....

Quote:

Apart from that, there's already a device that solves Ulf's problem: it's a long lever with a button on the front, usually located between the driver and passenger seat.

Do you mean the "quick-turn grip"?