These AEM X series gauges feature analog and digital readouts for quick interpretation, peak recall buttons, and user-selectable threshold warnings. Here’s the installation with the console trim back in place. The analog and digital readouts make reading the gauges quick and easy.

Oil pressure and water temperature are probably the most important things to monitor in a racecar, and if you’re allowed to play with air/fuel ratio, a wideband gauge is a must.

We reached out to AEM Electronics in Hawthorne, Calif., which supplied three gauges for a new Spec Miata build. The idea was to do a bulletproof installation, do it right the first time, with no need to go back under the hood or dash to correct something we missed.

We succeeded on that front and learned a lot along the way, the first of which was the importance of a common power source and a common ground. We’ve worked on cars in the past where each gauge was wired to a different power source and grounded ostensibly wherever the installer could find negative earth.

We picked up a six-way blade fuse box from Amazon for $9.25. It has four holes for mounting it, though we really only needed one, a common power pole for all six male blade connections, receptacles for blade fuses and LEDs that indicate a blown fuse. We had to supply the 5-amp fuse for each gauge.

Using that fuse panel, we could power it once, then run all three gauges from it. A simple, centralized power source. For a ground, we ran a leftover factory bolt through metal frame on the dash that bolted to the chassis. That provided the negative earth we needed to ground all the gauges, which all have a ground wire.

It’s important to note that the AEM gauges have a lot of extra wiring for use with things like the AEM Infinity controller or data logger, so we had to “cap off” the other wires so they wouldn’t accidentally touch something metal and go to fritz.

The installation couldn’t have gone any better. The directions AEM included were essential, and they were presented in a way that made things simple and easy to understand. Here’s how the installation unfolded.

This six-way blade fuse box from Amazon has a common power pole for all connections, receptacles for blade fuses and LEDs that indicate a blown fuse. We used 5-amp fuses for each gauge.
Advanced Autosports sells a filler panel for the console on a Miata. We drilled three 2 1/16-inch holes to accommodate the AEM gauges.
The hole saw leaves a messy finish. It’s easy to clean up the hole with a rounded file.
That’s better. Measure twice and drill once so your gauges are spaced properly and evenly. Note the nice edges that resulted from filing.
One of the coolest features on the AEM X-Series gauges is how thin they are. Remember when gauges required a lot of clearance behind the dash panel? No more. They protrude behind the dash panel less than an inch.
AEM X-Series gauges feature interchangeable black and silver bezels. We went with silver bezels for water temp and oil pressure, because that’s where we want our eyes to go first. The water temp gauge is closest to the driver.
You want gauges to power up with the key, so you need a power source that does that. The existing factory radio harness provided the hot wire we needed.
We needed to cut the wire from the factory harness so we could crimp an eyelet on the end to attach it to the power panel.
A good wiring tool is a must for this job, which reminded us that the wiring tool we have is not good.
Put the shrink wrap on first, then crimp on the eyelet connector that goes over the power pole.
A propane torch is a little overkill for shrink wrap, but it heats up faster than an electric heat gun. Use due caution.
Mount the power panel and connect the eyelet. A test light says we have power!
There is little common ground in Washington, D.C., but we can find it in a racecar. Using a leftover bolt and two nuts from the build, we have a stud where we can ground all three gauges.
The factory downstream oxygen sensor has to come out and get grounded. We made this bracket by welding a bung into the end of some 1-inch square tubing left over from the engine-based coffee table we made and bolting it to an unused chassis bracket.
The AEM temperature gauge comes with a sensor. We sourced a one-eighth-inch NPT bung and had it welded to the thermostat housing.
The AEM oil pressure gauge comes with its own sensor, which threaded right into the factory hole.
NA and NB Miatas have a nifty little hole on the driver’s side of the firewall. You can route the temperature sensor and oxygen sensor harness through here.
Put foil tape over the hole and around the harnesses. If there’s a fire under the hood, it won’t pass through the firewall, which is kind of the point of a firewall, right?
As mentioned, the AEM gauges have ample wiring harnesses, and some you don’t need if you’re not running an Infinity ECU or data logger.
This is where we needed to review the instructions. Everything outside the dotted line is optional. All we needed to connect was red to power and black to ground, and we already laid the “groundwork” for that.
Use your wiring tool to strip the ends of the red and black wires that come from the gauges.
The red wire gets a female blade terminal to connect to the power panel and the ground is an eyelet to go on the ground stud.
We connected the power leads for the gauges to poles 4, 5 and 6 and put all the ground wires on the one stud. An illuminated red LED indicates a blown fuse.
We used the metal wire ties that came in the box to bundle the wires so they’d be a little more orderly behind the dash. The right way is to cut the harnesses all back and use only what you need, but we had the room behind the dash and it was easier just to bundle them up.
The connectors that go into the back of the gauges are simple. Just snap them into place.
Before you button everything up, turn on the key and you should have gauges. We did and, uh, we did.
Here’s the panel installed without the console trim in place.
These AEM X series gauges feature analog and digital readouts for quick interpretation, peak recall buttons, and user-selectable threshold warnings.
Here’s the installation with the console trim back in place. The analog and digital readouts make reading the gauges quick and easy.
When you open a gauge box, you’ll find a likeness of what looks like comedian Patton Oswalt, but it’s actually John Concialdi, the founder and chief engineer for AEM Electronics. The company put his image on the inside flap as little “Easter egg” for customers to find. You’ve got to love a company with a sense of humor.
Image courtesy of Eric Green

1 COMMENT

  1. Brett:
    Couple “inputs” inspired by your article: 1) A lot of gauges are sold w/NPT fittings (A/M), and w/o a TIG welder, while more current vehicles come w/metric fittings that need to be sourced from Pegasus, Amazon or ACE ironically. 2) The square hole in the f/w should have been taped or plated over and a round hole w/grommet used. Why? Looks ugly to your friends and you were/are concerned with having FIRES, right? 3) Bundling w/cheap METAL ties instead of zip-ties? Same as #2. Please don’t assume I’m some random smart-ass looking to insult. Just passing on what I learned attaching a trio of gauges to the center console on my Mk6 GTI. Thank you,
    James R Kujawski
    Retired Mechanical Designer

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