Mark VIII Digital Dash

The speedometer on my 1993 Lincoln Mark VIII works when it feels like it. Lately it feels like it less and less. The rest of the cluster is fine, which means the one gauge I actually watch while driving is the one that lies, and I’m expected to just live with that.

The car itself is a project car, which is the polite way of saying a list of problems landed in my lap wearing a Lincoln badge. There’s a misfire I can’t for the life of me track down. The speedometer is just the one that talks to me the most.

The obvious answer to a bad speedometer in 2026 is to plug a scanner into the OBD2 port and see what the car thinks it’s doing. I don’t have an OBD2 port. The car was built in 1993, and it’s older than the connector everyone’s advice assumes you have. No amount of knowing your way around a car adds a port it never came with. Every answer on the internet for this starts with a step I physically can’t perform, and ends there. The internet’s universal advice stops at the door of my car.

What I have instead: the dashboard itself, an Arduino Uno, a Raspberry Pi, a dream, several other cars I could be driving while I make this one worse, and a specific kind of stubbornness about a gauge I didn’t buy a car to argue with. None of those is a solution. Together they’re the start of one — in the sense that a pile of lumber is the start of a house.

So this is the plan, and the plan is mostly a list of things I don’t know yet. I don’t know where the car actually measures speed, or what the signal looks like when it leaves the wire. I don’t know whether I can tap that signal without breaking something that costs more than the car. I don’t know how to power a microcontroller in a car without setting the car on fire, which I’ve been told is the kind of thing you want to get right the first time. And I don’t know how to make an LCD look like it belongs in a 1993 Lincoln instead of in a science fair, which is the difference between a dashboard and a box with a screen on it.

That last one is the one that’ll decide whether this works. The electronics either work or they don’t, and I can fix either. But if it looks like a prototype, it’ll look like a prototype for the rest of its life, and the car deserves better than that. The car is the only thing in this project that knows what it’s doing.

I’m going to learn all of it in the wrong order and make it work anyway, and I’m writing it down as I go so the next idiot who owns one of these and a box of microcontrollers doesn’t have to start from my notes. The engine misfires and I’ve decided to spend the weekend on the dashboard, which isn’t a fix, it’s a statement of priorities.

Nothing is wired yet. Nothing is decided yet, except that the speedometer and I are no longer on speaking terms, and one of us is leaving the car.