The idea that kicked this off is one many of us share: keep a classic looking completely stock while giving it modern behavior underneath. Dave's Garage pulled that off on a black 1970 Lincoln Continental Mark III by tucking addressable strips into the narrow space under the trunk lid, where they serve as a third brake light.
The heart of it is a custom red PCB labeled 'ThirdBrakeLight', complete with a 2020 copyright notice. An ESP32 module carrying a small integrated screen interprets the car's combined 12V brake and turn inputs, fed through four optocouplers and screw terminal blocks. Around those sit resistors, a diode, and electrolytic capacitors, plus an LM2940-5.0 linear regulator handling the supply side. With automotive power wandering between 11V and 15V, that strikes me as sensible margin. An EasyEDA schematic lays the regulator circuit out in detail, and the maker offers board fabrication through JLCPCB right from that tool.
The firmware is where this gets clever. Older vehicles route brake and turn signals through shared rear filaments and carry no CAN bus, so a state machine watches the timing between the left and right circuits and works out what the driver intends. The payoff is animated red braking that spreads outward from the middle and pulses between brightness steps without ever cutting to black, alongside amber turn and white reverse lighting. A garage show mode alternating red and blue hides in there too, and the whole design has to comply with FMVSS 108.
The interesting trade-off is that inference itself: rather than reading intent directly, the system has to deduce it from timing alone. It is also a clear step forward from the maker's earlier 1970 GMC truck build, which relied on mechanical relays; this time optocouplers won out thanks to automotive voltage transients and spikes. Anyone curious can go further, since the code lives in a public GitHub repository.
Project by Dave's Garage. Watch it on their YouTube channel: