Headlight Mod For An Audi A3

If you have a car that is getting on in years, it may be missing some of the latest frills and features that the latest models sport. [Muris] has a slightly dated Audi A3 8P which did not have an AUTO setting for the headlights. In the newer models, this feature turns on the headlights when the ambient light falls below a threshold level (overcast conditions or when going through a tunnel), or when the windshield wipers are turned on. The light sensor is integrated behind the rear view mirror in a special mount, requiring an expensive windshield upgrade if he were to opt for the factory retrofit. Instead, he decided to build his own Automatic Headlights Sensor upgrade for his Audi A3.

His local regulations require the car headlights to be on all the time when the vehicle is in motion. So adding this feature may seem moot at first sight. But [Muris] programmed the headlights to be powered at 70% during daytime conditions and switch to 100% when his sensor detects low ambient light conditions. In the power save mode, all of the other non-essential lights (number plate, tail light) are also turned off to hopefully extend their life. He achieved this by using the VCDS (VAG-COM Diagnostic System) – a widely used aftermarket diagnostics tool for VW-Audi Group vehicles. His tiny circuit switches the lights between the two power settings.

His plan was to install the device without disturbing the original wiring or light switch assembly in any way. The low-powered device consists of a PIC micro-controller, an LDR (light dependent resistor) for light sensing and a low current relay which switches between the two modes. Setting the threshold at which the circuit switches the output is adjusted by a variable trimpot acting as a voltage divider with the LDR. [Muris] wired up a short custom harness which let him install this circuit between the default light switch and the car electronics. After switching on power, he has 15 seconds to enable or disable his unit by toggling the light switch five times, and that status gets stored in memory. The tiny board is assembled using SMD parts and is protected with a heatshrink sleeve. The circuit would work equally well with a lot of other cars, so If you’ve got one which could do with this feature upgrade, then [Muris] has the Eagle CAD files and code available for download on his blog.

Check out the video below where he runs a demo, describes his circuit in detail and then proceeds to assemble the PCB without using a vise or a third hand to hold the PCB. That’s a fancy watch he’s sporting at 00:50 s down the video.

24 thoughts on “Headlight Mod For An Audi A3

  1. “If you have a car that is getting on in years, it may be missing some of the latest frills and features that the latest models sport.

    “[Muris] has a slightly dated Audi A3.”

    Slightly dated is a 2007 vehicle? Roughly 11 years old is only slightly dated? What do you consider actually dated? Doesn’t have OBD? Cannot find many parts for it? It’s interesting how complicated cars actually produced in the last 3 or so years are, even compared to ones from 8 years ago or so.

    Interestingly, the A3 was made for 9 years before being refreshed to the Typ 8V in 2013. Are the cycles of vehicle refreshes slowing down or speeding up here? Or is this just an Audi thing?

    “That’s a fancy watch he’s sporting at 00:50 s down the video.”

    1. In very few places of the world is a 2007 car considered old. I bet you that there are more cars on the road older than 2000, than younger than 2000. Bear in mind that very few of the people on the planet (less that 5%) live in the United States, and than by far the majority of the worlds cars and roads are not in the US.

      Even in the US, a 2007 car is dead on average age : http://news.ihsmarkit.com/press-release/automotive/average-age-vehicles-road-remains-steady-114-years-according-ihs-automotive

      1. Audi’s here in Sweden can have more basic features then even normal VW’s. I can’t understand the concept at all because in the US Audi is a luxury brand with all the luxury features. I was just car shopping recently and the A4’s at the same price range as the Passat’s were definitely missing the nicer features. That being said my 2008 A3 8p has auto headlights, Xenon headlights and the nicer rear view mirror with auto dimming. Undoubtedly this was a package that he is missing and would be an expensive retrofit.

  2. An interesting addon. But I have the headlights on all the time when driving anyway. A better mod is to have headlights auto off when you turn the car off and open the drivers door. Then you can leave the light switch on all the time. Headlight in the day time assist others to see you, particularly if you are approaching from the sun-ward direction. I often see folks driving their cars with just the parkers on when it is getting dark. They can see ok so they think that is ok. Headlights on all the time while driving is safer.

    1. yep my BMW (slightly dated 2003 vintage) has auto lights, I have tinted the sensor so they stay on all the time the cars running except for the most absolutely sunny days.

      a big issue with driving lights (headlights at reduced power and no rear lights) is people dont realise they haven’t put their rear lights on at night, this happens a lot, perhaps it’s a UK thing? but if headlights are on rear marker lights should.be on as a minimum imho.

      1. Yeah – Had an 2012 Aygo without auto lights – frogot it a few times – The only indicator that was to remind me to turn the lights on, was there were no light in the speedometer and radio until you turn on the lights

      2. No this happens in the US now that most new cars are like this. The even worse part is the daytime running lights tend to be the high beams at slightly lower power. So these people are driving with ~60% high beams and no other lights on. It’s really annoying.

    2. I have daylight running lights (DRL) in my 2009 car. We had the strange situation, that headlights-on or DRL was mandatory for some years, but luckily this was ended again. DRLs are OK, but I find headlights on in the day (especially in bright sunlight) quite annoying. Reflections of the sun are enough blinding light, we do not need more. Particularly if somebody approaches from sun-ward.
      Another consequence of this annoying headlight-on at all times is, that people do not switch on the other (rear) lights in a tunnel, because the headlights are on anyway. This is as annoying as “parkers-only”.
      Anybody who is not able to see a car during daylight without extra illumination shall get his vision checked.

      So if you want to use light during the day, please get proper DRLs or at least dim the headlights down like the author of this article.

      1. strongly disagree with the sentement of your post. most vehicles with LED DRL’s are absolutely blinding at night , however dip beams (which I drive with on 100% of the time) are perfectly fine at night. DRL’s are as dazzling as full beam headlights at night. but no manufacturer (or person) woudl drive around with full bam headlights on during the day.

        Dip beam headlights are designed to be used at night, and are barely visible during the day. I got into the habit of running them during the day as when driving a small or low car like an original MINI, or triumph spitfire, it did help other road users notice you in wet or foggy conditions , as are common here in the UK.indeed even in mormal size cars in the wet, if they are silver or grey, running lights helps a lot.

  3. “If you have a car that is getting on in years, it may be missing some of the latest frills and features that the latest models sport.”:

    So is it a car with a computer, or a computer with a car attached?

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