Retro Gauge Glory: Installing a Classic Instruments Custom Gauge Cluster


Retro Gauge Glory: Installing a Classic Instruments Custom Gauge Cluster


Earlier this year, Motor Life showed you how to order a custom gauge cluster from Classic Instruments. We wanted to give you an idea what their team of engineers and artists are capable of when you provide them with a direction and turn them loose.

We did just that with one of the least-likely vehicle candidates we could come up with: a 1976 Dodge Charger. While earlier generations of Charger are a relatively common sight at most types of automotive events, the fourth-generation Charger – as well as other 1975-79 Chrysler B-bodies – don’t get much love in the vintage-car world.

The Charger's shabby original gauges simply weren’t up to the task of providing information. The temperature and oil pressure gauges were non-functional; the fuel gauge was inaccurate; and the ammeter was a potential hazard. Even the NOS speedometer that was installed in 2021 was coming apart.

Unless you have a big-block car or a police-spec vehicle, chances are good that your first instinct would be to croon something about “rich Corinthian leather” when thinking about one of these Malaise-era Mopars. But from where we sat, that made this the perfect challenge for the Classic Instruments team.

We pulled the complete Rallye gauge cluster from a 1978 Dodge Magnum that desperately needed to be restored, and shipped the assembly to Classic Instruments’ Boyne City, Michigan headquarters. Once the cluster arrived, the Classic Instruments team photographed and disassembled it.

To remove the gauge cluster from a 1975-79 B-body Mopar, the dash must come apart. That means the metal “top plate,” the padded dash cover, the gauge faces (top and bottom), the HVAC panel, the radio, the controls for the side mirror – all of it comes out of the car. Your experience may vary depending on your particular make and model.

Then we worked with the Classic Instruments team to come up with a stock-appearing face for the gauges, along with a few upgrades: We wanted a 140-MPH speedometer. We wanted to convert the ammeter to a voltmeter in the name of safety.

And we wanted to modify one of the four “idiot lights” so that it would read “REVERSE” for an upcoming modification – in the theme of earlier Chrysler muscle cars that used a warning light mounted to the dash structure like an afterthought.

Before you start ripping into the wiring, make sure you have plenty of reference material on hand. Classic Instruments will provide a simple, straightforward schematic for the gauges. We recommend also locating a shop manual or factory service manual that has excellent schematics. We have the full factory service manual set for our Charger, which proved to be an invaluable resource.

We also decided to take advantage of Classic Instruments’ red-green-blue backlighting system, so that we could switch gauge colors when we felt like it with a remote control.

While we did have to wait a while for the work to be finished, it was all worth it when the delivery driver dropped off the big box filled with the rather sizable cluster for the Charger. Included with the kit were connector bodies and pins, Classic Instruments' SN16 speedometer sending unit, the signal filter unit, temperature and oil pressure sending units, a GM-style oil-pressure sending unit adapter, the calibration button switch, and the removed parts from the Magnum cluster.

Included with the modernized cluster are connectors and pins that make wiring a breeze. Just strip the end of the wire, crimp the pin onto the wire, then push the pin into the proper location on the connector.

Also included was a very clear schematic for the new cluster’s wiring and connectors – an important element in this project, no matter who’s doing the actual work.

While each vehicle application will have variables from make-to-make and model-to-model, the basic premise is the same – you need to disassemble your dash to the point where the gauge cluster can be removed. Next, you need to verify every electrical lead and how it operates. For that, we highly recommend using a factory service manual for your vehicle or acquiring high-quality schematics for your car.

You might find yourself scared to cut the first wire. If so, then now might be the time to find a reputable shop to do the work. That’s not to say that installing the gauges is a difficult task – far from it. Just be honest with yourself about your limits before you proceed to alter your electrical system.

If you find yourself sweating profusely at the thought of cutting into your car’s existing wiring, you may want to find a reputable shop that can handle the work instead. But if you’re confident to move forward, then rest assured that the connection part of the installation is simple – just use the provided pins to terminate the wire ends, and then secure the pins into the connector bodies as shown on the provided schematic.

You’ll need to provide 12-volt key-on power to the gauge cluster and to the signal filter, along with solid chassis grounds to several points, including the gauges, the signal filter unit, and the calibration button. Classic Instruments recommends running a separate key-on 12-volt connection to the speedometer separate from the others to eliminate any electrical noise in the signal.

Sure enough, upon disassembly, we found that our concerns over the ammeter were validated. The red/white and black/white wires at either the bottom for vertical or right for horizontal with wires on top are the ammeter leads, and on the black/white wire, there is scorching on the contact that connected with the original dash’s circuit panel.

Our Charger had one major modification that needed to be performed – an ammeter conversion. The ammeter gauge and their respective wire bulkhead connectors at the firewall are known problem points with these cars.

The conversion involves taking the positive and negative gauge connections and connecting them together, bypassing the firewall bulkhead spade connectors, and running a new charge wire from the alternator to the starter solenoid on the firewall, which will allow current to flow back to the battery.

While that is only pertinent to our installation, be aware that there may be similar issues that you’ll have to deal with if you upgrade to an aftermarket cluster.

Provided with the dash are an oil pressure sending unit (shown here) and temperature sending unit that simply replace the original ones. We opted to run signal wires from the sending units directly to the gauge leads, bypassing the firewall bulkhead connector.

Although an experienced electrical tech probably could have knocked out this installation in just a few hours, we did the right thing and took our sweet time installing the new gauges into our Charger, making certain before every wire got cut and placed.

This meant that when we reconnected the battery and turned the key, we had zero surprises – in fact, we managed to fix a couple of flaws that weren’t related to the cluster along the way!

The speedometer drive cable’s work is over. Replacing it is Classic Instruments’ SN16 speedometer signal generator and speedometer signal filter. Simply screw the SN16 into where the cable used to be on the transmission, run the wiring to the filter, and make the electrical connections. No more bouncing speedometer, no more cable noise.

The final step is to calibrate the speedometer and tachometer. Using the provided button and the instructions that Classic Instruments provides, calibration is a straightforward affair. Once in calibration mode, the tachometer can be calibrated based on your vehicle’s tachometer signal source, and the speedometer can be calibrated via one of three different methods.

Being able to see your gauges at night is critical. For some, gauge color doesn’t matter too much; for others, it’s everything. With Classic Instruments’ red-green-blue LED backlighting, you can change the color of your gauges on the fly. While we’re partial to the almost stock aqua-green, the range of colors available should satisfy anyone. The LEDs aren’t blindingly bright, either.

Once you’re content with how your gauges operate, reassemble your cluster – in our case, back to stock – and enjoy. Our Charger’s gauge interface is a dramatic improvement from the original gauge cluster. Our speedometer doesn’t bounce like a 6.7-magnitude earthquake, our fuel gauge has a truly accurate reading, we have functional temperature and oil pressure gauges, and having a tachometer on-hand takes the worry of engine stress off our mind during Interstate travels.

There may be certain tasks that you need to fix or sort out before installation is complete. In our Charger’s case, we had to perform an “ammeter delete,” which reroutes the electrical path of the car. We won’t get into the details of what that requires, but just be aware of what your situation may demand.

It might seem like radical overkill for a mid-1970s sled that hasn’t seen one engine modification yet, but a fully functional gauge cluster provides amazing peace of mind. If you want custom style and functionality for your gauges and Classic Instruments doesn’t offer one of their Direct-Fit clusters for your vehicle, consider their Custom Design Service.

Or, if you don’t want to go that far and just need accurate gauges, look at Classic Instruments’ Retro-Fit Design service, which takes your provided cluster and fits your standard gauges with electronic movements, giving your project modern capability without losing that classic look.

Either way, there’s simply no excuse for driving around with non-functional gauges anymore.

Check out the full Classic Instruments product line now at


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