The first step is to remove the existing dash-speedo cluster. Begin by disconnecting the negative battery cable. Then loosen and lower the steering column, disconnect the speedo cable, and unplug the instrument-cluster harness. Next remove all attaching fasteners to take out the dash-speedo cluster. If needed, OPG offers Chevrolet service manuals for early Chevelles. You may want to tag the wires where they plug into the cluster to make them easier to reinstall.
With the speedo cluster on a bench and apart, scribe the rear of the instrument housing for cutting with the supplied template. There are also three 1/8-inch holes marked on the template that need to be drilled.
With a saber saw or small grinder, remove the metal sections from the housing as outlined and drill the three 1/8-inch holes.
After cutting, the instrument cluster should look like the lower housing. Shown above is an uncut instrument housing originally designed for warning lights.
From the front, all the gauges are identical in appearance to the 66-67 units.
For better reliability and ease of hookup, OPGs BATT instrument is a voltmeter, unlike the factory-original ammeter. The oil-pressure gauge is operated electrically, unlike the original mechanical unit.
Now the gauges are ready to install in the positions that held the old fuel gauge...
...and the clock, or block-off plate.
The red wire connects between the two separate gauge terminals marked red."
The black ground wire attaches to both gauges and also to the two 1/8-inch holes previously drilled in the instrument housing. Grounding the instrument cluster to the body is also recommended. Now the cluster and other items previously disassembled can be reassembled.
The OPG gauge kit uses electrical sending units for both oil pressure and engine temperature. The kit uses sending units for a 75 Firebird with factory gauges (available from most auto parts stores). To connect the gauges, attach the green and blue wires (included in the kit) to the terminals marked grn and blu. Then route the two wires through the firewall and to the new coolant-temperature sending unit (green) and oil pressure-sending unit (blue).
The new gauges have that factory look. To supply power to the OPG gauges, install the plastic connector that was attached to the old fuel gauge to the rear of the new fuel gauge. The new red wire supplies power to gauges on both sides of the cluster. Finally, reinstall the cluster and subsequent parts back to the dash. Remember to install all the gray wires and bulbs (dash lights) into the housing. This 67 Chevelle also needed a new speedo cable so we contacted OPG for the right part.
OPG offers a neat tachometer for 67 Chevelles that includes the left-hand turn signal. The tachometer comes complete with a wire harness. To install the unit, connect the red wire to a switched terminal at the fuse block. Next, connect the gray wire to the dash-light harness and the blue wire to the left-turn-signal harness under the dash. Finally (on point-type distributors), connect the brown wire to the negative side of the coil. On HEI units, this wire connects to the tachometer terminal. On certain ignitions, a special tachometer adapter must be used. We used one from Crane. CHP