The no. 1 question I’m getting about the HW4 retrofit is “omg why did it require a new windshield??!” The answer may surprise you: it didn’t. I hadn’t planned to replace it, but the original broke, and a Highland windshield was the easiest way forward. Details below. The obvious differences between the HW3 and HW4 forward-facing cameras are their number and size. HW4 uses 2 larger cameras + 1 placeholder; HW3 is an integrated unit of 3 cameras with much smaller sensors. HW4 also has a completely different mounting-hole pattern. But the real problem was the size and placement of the temperature/humidity and light sensors. The HW4 sensors wouldn’t fit in the HW3 frame, and the HW4 frame wouldn’t fit the HW3 windshield because of the light sensor cutout’s location. My plan: 3D-scan both frames, then design and print one that fits the HW3 windshield, accommodates the HW4 sensors, and accepts the HW4 outer shell. No glass changes. Solid plan, and relatively simple, too. One day later, I’m driving on a freeway when a rock shoots out from under some truck’s tire and cracks my windshield. Not exactly pleasant, but a week later, my Tesla was rocking a Highland windshield with its stock HW4 frame and heaters. No going back now. Luckily, the unbeatable @Tutrifour had already shipped me a full set of Highland windshield and interior cameras, plus the rear-view mirror assembly. After giving the adhesive a day to cure, I started installing everything. A 15-minute job, surely. You would not believe just how wrong I was. The windshield unit included its original harness, running from the cameras and sensors to the lower A-pillar connectors. I swapped the stock harness for it to avoid squeezing FAKRA-Z adapters into the cramped windshield assembly or cutting keying tabs off aluminum connectors. One of the worst decisions of the entire project. Only after laying out the whole harness did I discover that Tesla engineers, likely just for teh lulz, had swapped the male and female sides of the quad mini-FAKRA connectors in the lower A-pillar. As planned, no adapters under the windshield. Bonus: two harness halves I couldn’t physically connect. Many cut coax cables and even more swearing later (crimping RG58 connectors will do that), the new cameras were connected to the computer. And they didn’t work 🙃 I’ll spare you the investigation details. Let’s play a game instead! You’re interviewing for an electrical engineer role at Tesla, working on the Model 3 Highland refresh. The old Model 3 has 4 cameras on the windshield and a GPS antenna. Its harness splits in the lower A-pillar: the cameras share a quad mini-FAKRA connector; GPS gets a separate full-size FAKRA. Nothing unusual. The refresh has one fewer camera, so one fewer cable. Your first task: redesign the wiring. What do you do? If you said “leave one position in the quad connector unpopulated to keep things simple,” congratulations — you failed your Tesla interview. That’s not wrong; it’s just the tip of the iceberg. The only valid answer: “Leave one position unpopulated, randomly shuffle all the connections, move the main camera to the separate full-size connector (keeping the same FAKRA key and color), and put GPS where the main camera used to be. Oh, and swap the male and female sides and change the keying so no sane person could even think about retrofitting this stuff.” I’ll refrain from commenting on that. Fun fact: the Highland windshield harness is much larger than the old one. There was no way to click the headliner into place without completely covering the interior cam. Cutting off a large piece of the interior trim is one of the things that definitely weren’t on my bingo card for this project.

This is the world’s first and only* legacy Tesla Model 3 retrofitted with FSD Hardware 4. It also happens to be my car! The story begins a few months ago, when – inspired by @mikegapinski’s efforts to launch FSD in Europe – I’ve started digging around my Tesla’s infotainment and related systems, their security, and reverse engineering of all the firmware artifacts I could get my hands on. At that point I still had no idea how deep into this rabbit hole I was eventually going to wander and how many hours of sleep it was going to take away from me. This was my first hands-on experience with FSD and, albeit still awfully impressive, v12 on HW3 was not the chauffeur experience I was hoping for. I knew Tesla wasn’t going to offer an official retrofit option, ever, and starving for a new adventure, I slowly started looking around Tesla’s official car schematics, comparing different variants of HW4 computers and mapping signals between HW3 and HW4 connectors. It quickly became clear that it was not going to be a weekend project. Not really enthusiastic about the odds, I shifted my focus onto other areas of the car—mainly the MCU itself, deep RE of both the hardware and the software, and learning as much about its internals as I only could. Two months pass by, I’m leaving on vacation with my wife and kids. Destination: LA. Rental car: FSD-subscribed Tesla Model Y, Juniper. Of course. I knew it was going to impress me. I did not know it was going to blow my mind. And sure as hell I did not expect it to impress my wife too (which is not an easy task for anyone or anything, trust me on that). During our wonderful two weeks there we’ve done about 2k miles in the Tesla. Out of those, I don’t think we’ve driven more than 30 miles ourselves, combined. All the rest, including a trip to Vegas and back through the Death Valley, was FSD v14—with not a single disengagement, even in rough conditions and poor visibility. Back home, it became clear to me. I’m either buying a new car or retrofitting HW4 into my Model 3 so that I could experience real FSD at all times. If you’re reading this, you know which path I took. Want to learn more about the retrofit process and how it all came together, what issues I experienced along the way, and how I managed to make it (nearly) all work? Drop me a follow, I’ll be sharing much more details in the coming days and weeks. And, spoiler alert, that retrofit is just the beginning 😈 * - that I’m aware of — but I don’t think anyone else in the world is mad enough to have tried that