Upgrading GM Squarebody Gauges With Classic Instruments' Direct-Fit Gauges


Upgrading GM Squarebody Gauges With Classic Instruments' Direct-Fit Gauges


We recently converted a 1982 Chevrolet C20 into the ultimate roadside service rig in order to assist any and all fellow hot-rodders that might run into car trouble while participating in the hugely popular Hot Rod Power Tour. In addition to using a host of Holley’s swap products to replace the worn out old small block with a refreshed LS, we also wanted to upgrade the gauges with a modern, electronic cluster from Classic Instruments. These gauges for the 1973-1987 Chevrolet and GMC trucks are a direct bolt-in swap, have a seven year warranty, and work with many different engine combinations with just a little bit of wiring to adapt them to your truck's harness.

Sally's Speed Shop C20 Classic Instrument Gauges

If you want the modern reliability of electronic gauges but don’t want to build your own custom dash or lose that OEM look, these gauges are the perfect fit for your vehicle. The 1973-87 Chevy/GMC direct-fit cluster features a speedometer and tachometer, and fuel, oil, temperature, and volt gauges in our near-stock OE Style. The all-electric cluster arrives ready to install directly into the stock dash of 73-87 trucks, Suburbans, and Blazers, with ease. Simply replace the factory connector with the new connector included in the kit. Better yet, these gauges are designed to re-use the factory dash bezel and gear indicator to maintain the nostalgic integrity of the vehicle, and the turn signal indicators are even in the factory location

The cluster is designed to reuse either the stock fuel sending unit or just about any other aftermarket fuel sender with the built-in ohm range selector switch and can be used with just about any engine combo simply by selecting the correct sending units for your project. They are available in a variety of different gauge faces so whether you want to freshen up your stock look, or make your own custom gauges like we did with ours, the 1973-87 Chevy/GMC direct-fit cluster offers the finishing touch to any custom build or restoration.

Sally's Speed Shop Classic Instruments Direct-Fit Cluster

The OE Style 1973-87 Chevy/GMC direct-fit cluster features a speedometer and tachometer, and fuel, oil, temperature, and volt gauges. Everything needed to install the package is provided in the kit, including a new lens and all of the necessary sending units. This is really is about as simple as a gauge install can be.

Follow along as we show you what it takes to easily upgrade the gauges on a Squarebody-era truck with this super easy installation.

Sally's Speed Shop Gauges Custom Faces

These gauge sets are available in a variety of different face styles, and you can even get your own custom faces designed by the team at Classic Instruments. We opted to put our shop logo in our speedometer and tach for that extra, custom detail.

Sally's Speed Shop Gauges OEM Cluster

The first step in installing your new gauges (look at just how crusty the old ones were in our C20 project) is to simply remove the screws holding the dash bezel on, and then remove the four screws holding the factory cluster to the dash framework.

Sally's Speed Shop Gauges test-fit

Once you’ve removed the factory dash bezel it’s time to test fit the new cluster to it. The provided aluminum standoffs on the new cluster are adjustable, to help ensure a perfect fit in any bezel.

Sally's Speed Shop Gauges Fuel Sender Selection

Before installing the gauges into the dashboard, be sure to make sure the fuel selector switch on the back of the unit matches your fuel sender’s resistance range. In our truck, we were using a stock style GM sending unit which ranges from 0-90 Ohms, corresponding with position “2” on the switch.

Sally's Speed Shop Connector Plug

One thing we really like about the Classic Instruments gauges for Squarebody-era trucks is that there is a single plug that connects to the back of the cluster upon installation. There are no pesky control boxes to mount under the dash, making for a very clean and simple install.

Sally's Speed Shop Gauges Wiring Connector

Everyone has different opinions on how to make the correct type of connection when wiring, but we chose to simply use a metal butt connector with a crimp and a small piece of heat shrink to prevent bulky wiring under the dash.

Sally's Speed Shop Gauges Temperature Sender for LS

Once you’ve started wiring in the gauge harness under the dash you will need to run the wires to your various sending units. If you specify you have an LS engine, Classic Instruments will send you the correct temperature sender (p/n SN12MM) with 12mm threads that mounts into the passenger cylinder head near the rear of the engine.

Sally's Speed Shop Gauges Wiring

Wiring is a scary thing for a lot of people, but these gauges are about as easy as it gets. It’s as simple as matching up the correct color wire from the vehicle’s harness with the corresponding color on the gauge harness, much like installing an aftermarket stereo. We simply crimped the wires together with a butt connector and heat shrunk it to protect it.

Sally's Speed Shop Gauges Instructions

Classic Instruments even includes a very detailed instruction booklet that has a complete gauge wiring diagram that makes it super easy to match up the wiring for the gauges to the factory vehicle harness.

Sally's Speed Shop Gauges Oil Pressure Sender

In an LS-powered application, Classic Industries recommends you utilize an oil bypass housing from an LS1 to mount the supplied 0-100 psi oil pressure sender (p/n SN52) on your engine, just above the oil filter location. The LS1 oil bypass housing will need to either be drilled and tapped, or have an adapter installed to convert it to 1/8”NPT to match the supplied sending unit.

Sally's Speed Shop Gauges SN16 Signal Generator

Additionally, these gauges utilize a pulse signal to run the speedometer. In our situation, we installed a SN16 signal generator into the factory speedometer gear housing on our SM465 transmission and ran the 3-wire harness up to the back of the gauges under the dash. If you have a modern transmission, you can simply send a signal from the ECU to the gauges to run the speedometer instead.

Sally's Speed Shop Gauges Final Cluster Wiring

Once your wiring connections have been made, including creating a quality ground location for the harness, you can simply plug the connector into the rear of the gauges before installing them into the dash.


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