Pre-Facelift Tesla Model S LED number plate lights (WHL #70)

It’s time for cheap lights on expensive cars because of the friggen 3G mobile phone network. Yeah, that sounds perfectly alright.

Two weeks ago I ordered the MCU2 upgrade for my 2015 Tesla Model S at the Service Center Frankfurt. Ever since the possibility for that retrofit was announced by St. Elon, I lusted after it, yet of course it only was made available in the alternative Elon Time™ dimension on time and was delayed forever for everyone else, especially for AP1 cars like mine. Some day in between the recall bombshell of the MCU1 dropped and Tesla extended warranty of that part to 100k miles / 160Mm or 8 years max, and some months later the price for MCU1 cars was reduced from 2500€ (inclusive VAT) to 1550€ (same), as those do not need the AP3 computer refresh.

That whole shebang was a story of opting for something, then delaying or skipping it, until circumstances changed significantly. Initially, I was on my way to the Netherlands, to get the failing MCU1 chip replaced by Lucky Luke. In late January 2020 I scheduled for March 10th. The idea being a ~500€ replacement including 4G retrofit would be better than paying 2500€ at the SeC when flash wear would cause the computer to go tits up. That appointment got cancelled six days prior due to the MCU2 announcement. In November 2020 Tesla announced that the MCU1 got an extended warranty, and in February 2021 they were forced to by the NHTSA which caused another mass mailing (I was one of the owners complaining to them as “overseas resident”, mwahaha). They also prepared one last software update that would fix the major issues with everything going dark, e.g. heating and ventilation being stuck on their last setting.

And then 5G hit. On July 1st the last frequency bands of 3G were shut down in Germany within that day, and will be allocated to 5G gear instead in the near future. For a car that relies on connectivity, that either means a stuttering Spotify on 2G fallback, unusable voice recognition, and, well the browser was dead way before that, or using a hotspot device every time one enters the car, with the WiFi connection requiring attention after every park cycle. A third option would be the 500€ 4G/LTE retrofit without changing the MCU.

That wasn’t enough. I’m now past 160000 km so MCU1 extended warranty is void, and in early August a bubble started to form in the instrument cluster display. A day or two later it arrived at the bottom of the screen. No leaked fluid yet, but that sticky goo needed to go somewhere someday. Plus a new instrument cluster is around a thousand bucks. A new main screen is as well, btw.

So after all the inconvenience I pulled the trigger for the MCU2 retrofit. It’s now done but not entirely working, but overall I enjoy it despite the audio system becoming worse. I also lost AM/FM radio, but I never used in during the entire ownership to actually listen to radio, instead I only tapped it sometimes to get Spotify going again. I also got two new screens and the LTE modem. This time, nobody stole my USB charging cable, so that’s a plus.

What the fuck has this got to do with number plate lights?

Well, the camera retrofit (another 500€) is not included in the package nor is it necessary or even recommended unless the hardware has failed. (Most?) MCU1 cars apparently use a different camera than stock MCU2 cars. Not sure if they went from analogue to digital or just some encoding or voltage level stuff, but it’s different and needs some tiny converter thingy in between. When it first came out, people complained that it basically shows a black screen in the dark, nowadays the software fixed some of that (still no user-defined brightness or contrast). It still is significantly darker than the original, especially for European cars that use the second reverse light housing for the (sometimes mandatory) fog light, whereas US cars apparently have two reverse lights, left and right, so double the amount of light to begin with.

Now there’s the option to make a significant mod to the car in adding an external reverse light – or to cheat and turn up the number plate lights by a notch or two.

You see, the default lights up there are, get this: Incandescent bulbs. 2x 5 watts, left and right. Apparently shared with the 2007+ Mercedes C-Class W203 and some other Mercedes models. It is, if the parts have some “E” number on them to make them usable without additional paperwork, extremely easy to swap them to LED. So I did. For the very exclusive price of 16.99€ including shipping. Available on eBay and other marketplaces.

So here they are. Note the VERY important QC pass sticker that makes this a premium item.

It’s also interesting that the heat sink is somehow labelled “autolight24”, while the shop at that address currently does not sell these. There are a couple of variations on this type of light, and apparently it is very important to get the ones with the heat sink. It is, unfortunately, a vital part since those seem to be linear regulators aiming for a certain current instead of DC-DC converters or real current drivers, but more on that in a bit.

The front plate is not partially darkened as the original unit was, so there’s more illumination all around. Perfect for my intended application. Two screws out, swap the light, two screws in. Repeat for the other side. Use a flat head screwdriver even though these are Phillips screws of some non-EU standard size (hate these!)

One can’t really see all that much inside, but that 330R resistor was noticeable. So another indicator that this isn’t a pure current source running in the high 80s+ efficiency range, but some dumb linear regulator that needs limiting resistors and will handle all voltages that can be expected from a good ol’ lead car battery.

Here’s a graph on power consumption: It roughly stabilizes at 150-160mA beyond 12V (dips down to 150mA after some warmup period), so in real world use it should dissipate around 2 to 2.5 watts – less than half of the original wattage. It’s still very hot at 75°C in free air (ambient 20°C), so it might peak at 100°C in the car. That should be way less than was produced by the incandescent, so the parts around them will be fine, yet 100°C isn’t all that great for LEDs. Well, maybe a DC-DC driver is possible without the rest of the car acting up, but unless there’s one available with E number, I won’t give it a try.

I also got some FLIR footage of it, although readings are off due to the shiny metal surfaces. Scales are fixed 20-60°C. I checked temperatures with a contact thermometer to make sure.

For a quick comparison of incandescent and LED, I ran both units together in my usual setup (also colour temperature, so this is quite blue compared to the warm white LEDs used otherwise). This was taken at 13.5V, so somewhat realistic circumstances in a car. Although the LED only takes half of the wattage of the bulb and is facing down while the other is directly facing the camera, it is clearly brighter.

In terms of colour spectrum I’m very happy to state the those are good LEDs with a reasonable CRI. Check the spectrum below – a bit more yellow instead of blue would make it perfect, but it is a very “even” white light overall and also works well with the camera. Very satisfied after having low expectations!

And now the important part – does it work as intended? Yes, it does! Check those two images, reasonably resembling what one can see on the screen at 0% brightness:

What’s the difference? The latter shows the track overlay, meaning that one has the reverse lights ON. While the garage on the other side of the street is a bit brighter with them, the absolute majority of photons in the important parts of the picture are now from the number plate lights. Unfortunately I do not have a direct comparison of these since I swapped them in bright daylight, but an artist’s impression™ of what used to be present with MCU2 and the old lights is next; and this is even a nicer example since the pavement is bright concrete. On regular asphalt it was close to black even directly below the camera, which even caused me to park on the streets one rainy night since I do not like reversing by ear. It’s simply too expensive…(yes, the parking sensors do work fine for things farther away than 30cm)

So, verdict? Should have bought these ages ago! A very worthy 0.5ish ‰ investment in the car :lol:


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