Digital Gauge
Cluster

The engine got a new brain

The 4Runner doesn't run on Toyota's original engine computer anymore. It runs an aftermarket one called a MegaSquirt, and that little box pays attention to everything — how fast the engine's turning, how much air and fuel it's getting, how hard it's working, how hot it is.

Problem was, all that information had nowhere to go. You could plug a laptop into it and read the numbers, which is great in the driveway and completely useless halfway up a trail.

The old gauges couldn't keep up

The factory cluster gave you a speedometer, a fuel gauge, and a temperature needle with two settings: fine, and too late. That's about it.

When you've tuned the engine yourself, that's not enough to go on. You want to catch a problem while it's still small and cheap, not after it's already cost you something.

So we hooked the screens up to it

Two wires run from the engine computer to the new cluster, and everything it knows shows up on the screens. That sits right alongside the stuff the truck still tells us the old-fashioned way — how much gas is in the tank, whether a turn signal's on, if the back door's open, how cold it is outside, and where we are from a GPS antenna.

Two of those numbers are worth their weight in gold on an old engine. Air-fuel tells you if the tune is right where you're actually driving, not just at idle. Vacuum tells you how the engine's breathing, and it's usually the first thing to go weird when something's wrong.

And it still fits like it belongs there

It fits the factory opening, it's the right shape, and out of the box it looks like a normal set of round gauges. Nobody riding shotgun would think twice about it.

The modern stuff is hiding behind that. Swipe when you want it, ignore it when you don't.

The main screen

An 8.8-inch wide screen, 1920 by 480 — long and short, which is exactly the shape of the hole the factory cluster came out of. It's a touchscreen, and that's how you swipe between looks.

Running it is an ESP32-P4, a little dual-core chip on a development board about the size of a credit card. It's the one part in here doing real work: drawing a 1920-pixel-wide dash ten times a second while also listening to the engine, the GPS and the sensors.

The two round pods

Two 1.46-inch round touchscreens, 412 by 412 pixels, each with its own ESP32-S3 built onto the back. They're small, they're round, and behind a bezel they look like ordinary gauges.

One is set up as an inclinometer — how level the truck is, front-to-back and side-to-side. It has its own tilt sensor built in, so it keeps working even if everything else goes quiet. The other is the engine pod — vacuum and air-fuel, the two numbers that tell you how the engine is really doing.

Both run the exact same software. Which job a pod does is decided when it's plugged in, not when it's programmed, so there's only ever one version to keep track of.

The board we made

This is the part you can't buy. It's a 100 × 95 mm circuit board we drew ourselves, and it's the reason any of the rest works: 1986 wiring goes in one side, something the screens understand comes out the other.

A truck's electrical system is a rough place. The voltage swings, the alternator throws spikes, and every signal is designed around parts that stopped being made decades ago. Screens are the opposite — they want clean, steady, low voltage and they die instantly if they don't get it. Nothing off a shelf sits between those two worlds, so we made the piece that does.

What it listens to

A GPS and compass module up on the dash gives heading, position, altitude and the clock. A temperature probe behind the grille reads outside air. The truck's original fuel sender in the tank still does its job — we just read it differently. And the engine computer sends everything else down a single pair of wires.

All three screens update over Wi-Fi

Sit in the driveway, connect your phone to the truck, drop in a new file, and a couple of minutes later everything's running the new version. The big screen updates straight over Wi-Fi. The two round ones don't have Wi-Fi at all, so the main screen passes the update along to them through the wiring that already connects them.

That last part took some doing, but it means a screen buried behind the dash is just as easy to update as the one you can see.

It won't brick itself

Every update gets checked before it's installed. If the file shows up damaged, or the Wi-Fi drops halfway through, the cluster shrugs and keeps running what it already had. We tested that the hard way more than once.

And it fixes its own Wi-Fi

Early on, the Wi-Fi would occasionally lock up and the only cure was pulling power. Now the cluster keeps an eye on its own radio, and if it stops answering it restarts it — back on the air in about a minute, without anybody touching anything.

Everything on one board

The first version needed a hand-built adapter cable, a couple of resistors soldered on by hand, and two separate little boards for the pods. All of that is now part of the main board. One board, one set of connectors, nothing to remember.

The pods use the plug they already have

The round screens come with a twenty-pin ribbon connector on them. The new board has the same connector, wired pin for pin, so an off-the-shelf ribbon cable plugs straight in at both ends. No custom cables, nothing to make up, and nothing to get backwards.

A parking brake light

The 4Runner's original parking brake gets its own warning on the screens, styled to match whichever look you're running. The factory lamp doesn't come back — the new cluster handles it.

Room for two more pods, and spare inputs

The board drives the two round screens it has, and leaves connections for two more further away, so extra readouts can be added later without designing another board. Three general-purpose inputs are built in for whatever comes next — another sensor, another switch, something not thought of yet. Cheaper to include them now than to redo the board later.

It'll be able to make noise

There's a connection for a small speaker. The idea isn't beeping at you all day — it's the couple of things you'd want to hear about with your eyes on the road. Running hot. The engine going lean when it's working hard. A door open once you're rolling.

Deliberately not on the list: a turn-signal tick. The truck's flasher relay is the thing that clicks, it's still under the dash, and it still does. No point in two.

Fixes found the hard way

A handful of corrections that only turned up once the first board was built and wired: a connector with its rows the wrong way round, missing resistors that stopped the compass being seen, the fuel gauge reading off a pin that couldn't actually measure, and — the last one to show up — two small resistors for the turn signals.

That one is worth a word. The truck runs LED bulbs, and an old filament bulb quietly did a job nobody thinks about: it gave the turn-signal wire somewhere to drain to when the flasher clicked off. LEDs don't. So the dash light came on with the stalk and then just sat there, solid, while every wire in the truck measured perfectly fine. Two resistors on the board fix it for good, and they do no harm at all if you ever put ordinary bulbs back in. That's the kind of thing you only find with the truck in the driveway and the key on.