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.