How To Install a Boost Gauge

One of the great joys of life is experiencing the surge of horsepower from a turbocharger. It makes all of the sutututuuuu and pshhhh you could ever ask for when the throttle blade slices closed – it’s pure infantile joy. The only way it gets better is by having a boost gauge excitedly buzzing away in your peripheral vision as boost builds and releases. For that, I’m going to show you how to put a boost gauge in any car. 

There can be no greater service to the gods of 2000s car culture than installing a big old boost gauge in the cockpit of your machine. Luckily, it’s extremely simple and only takes a few tools and some cheap parts with a little ingenuity. 

First things first is acquiring a boost gauge. Options vary greatly because you can spend as little as $20 on a boost gauge from Harbor Freight to as much as $250 for the most Japanese Domestic Market (JDM) legit Défi gauges. The installation process for either one is more or less the same, so the choice is mostly down to quality and aesthetics

There is one important distinction that separates all boost gauges: mechanical and digital. A mechanical boost gauge uses a boost reference to physically move the needle in the gauge. A digital gauge takes a boost reference into a sensor which sends data to the gauge via wiring and displays it on a screen or with an analog dial via a stepper motor.

Mechanical gauges have amazing response and accuracy (once calibrated correctly) and are simple to install. The accuracy and response of digital gauges, however, varies greatly. Cheap digital gauges can be slow to respond and inaccurate. In my experience, name brand stuff like Défi, AEM, Stack, and Greddy all have mechanical gauge response while having the style and diagnostic benefits of a digital gauge. Stuff like Prosport doesn’t quite match up. 

The main reason you would want a digital gauge over a mechanical is the ability to store peak values. This can be useful to see when you are under or overboosting. Digital gauges also have cool gauge sweeps on startup that add to the theater of starting the car. That’s not strictly necessary, but for a tuner boy like me it matters a lot. It’s why I have a Défi oil temperature gauge in my car.

For this install I’m going to be using a Newsouth Performance mechanical boost gauge, which means we’ll be doing some wiring and routing a boost reference from the engine bay into the cabin. This sort of work is more finicky than it is difficult, but it’s mostly straightforward and shouldn’t take more than a few hours. Before you begin, I would peruse the wiring diagram of your preferred boost gauge and start figuring out where you can splice into wiring on your car.

[Warning: For safety purposes when working under the hood and with wiring, it's a good idea to disconnect the battery terminals and to use safety glasses and gloves.]

This sounds scary because it is scary. This is the only permanent part of the installation, but it can be made as painless as possible with some connectors and bravery. At the very least, you will need some basic wiring supplies. I know that there are several schools of thought with wiring, but we’re going for cheap and easy, so I used basic butt (yes, butt) and spade connectors to do the job along with a wire cutter/stripper/crimper combination tool.

Every gauge will come with a small instruction pamphlet that breaks down how to install. The most important part of this will be the wiring diagram. Most gauges will have three to four wires, depending on the type of gauge. Because mine is mechanical, it has three wires for power, ground, and dimmer. A digital-type gauge will add one more wire for signal from the boost pressure sensor. The diagram will tell which wire is which — keep that in mind going forward. Also consider where you want your gauge to live in the car to determine wiring length and routing.

Take those wiring assignments and start digging through your own car for a suitable source of power, ground, and dimmer. For a power source, you want to use an ignition-switched source so the gauge turns off with the car. Ground can be installed anywhere there is metal, I usually choose a small bolt and an eyelet to ground my wiring. Alternatively, you can use the ground wire on the car’s harness if there isn’t any metal nearby. Dimmer is the only wire without free choice; usually there is only one dimmer wire for a given component.

For the purposes of this install, I’m unfortunately (for me) using my 2010 Volkswagen Golf GTI. Fortunately (for you), this means I’m doing this install on the most finicky vehicle possible. Most people will have cars with much simpler electrical systems. On any car, a good place to start for finding switched ignition power is going to be a headlight switch, a 12v cigarette lighter socket, or the radio. Some power sources can be constant and others switched on the same connector, so make sure to find the switched power. The best way to find out is with a wiring diagram and a voltage meter. 

Use the voltage meter terminal to probe the back of the connector where the wire goes in and ground it to some metal. If it shows no power when the ignition is off and 12 volts when the ignition is on, you have switched power. If it shows power regardless of ignition position, it’s constant power. I recommend always testing the wires you want to use regardless of what the diagram says. Often, the diagram is wrong, and it’s best to test things for yourself. You can also use this method to find a suitable power source by manually testing wires.

Now is the scary part. Unless you want to risk a bad connection by using a quick splice terminal, you must cut the wire. Quick splice terminals can be great but sometimes will not cut deep enough to make electrical contact. My low-buck technique of splicing into a wiring harness requires an old fashioned butt connector with heat shrink. I cut and strip the desired wire and place one end into the butt connector, then I get the other end of the cut wire along with the wire I want to splice in. I twisted the two together and place it into the other end of the butt connector. Crimp it down, shrink the heatsink and the job is done. Rinse and repeat, as they say.

I like to also add an individual connector to each wire for future serviceability. It would suck to have to cut and re-connect wires with a butt connector if the gauge had to come out. Some of you may ask why I’m not using solder and the answer is simple: Solder isn’t good under the vibrations and conditions present in a car. A crimp is much stronger and more flexible, even if it’s a basic one. I could have gone crazy and used Deutsch connectors, Raychem heat shrink, and done it “properly,” but this is low-buck and works fine for most of us.

The last thing to do is to route the boost reference line from the engine bay. A mechanical gauge will require the hose to run all the way to the gauge, while a digital unit will have a box that you can hide under the dash. Finding a boost reference should be simple: anywhere in the intake system past the turbocharger will give a proper reference. Most cars will have extra ports on the intake manifold. In my case, I purchased a boost tap that replaces a PCV hose connection and ran a catch can. Run the hose through a grommet in the firewall. Don’t be afraid to cut a hole in the rubber. Plug that in, and you should officially have a boost gauge.

I’d take a moment to start the car and verify everything works. If the gauge shows vacuum at idle and moves with a throttle stab, all is well. Check the dimmer and other functions, then think about where you want to finalize the gauge mounting. I chose the steering column for visibility, but some will mount in an air vent or in the center stack. It’s all up to you. Drilling shouldn’t be required, and I use 3M VHB double-sided tape to mount any gauge pods. For this install, I used a Newsouth molded column cover that fits over my factory steering column and has a mounting hole for my gauge.

Make turbo noises to your heart’s content. I love watching the needle go crazy and the child within most of us will too.