Forget The Bolt-On Tachometer, Now There's Retrogauge's Mini-Tach For 1967-68 Mustang.
Not so long ago, Retrogauge's Mike Brand sent me one of his Mini-Tachs for 1967-68 Mustangs for a quick how-to in Mustang Monthly. You can't beat this afternoon bolt-on/wire-in for ease of installation and a cool factory look. If your '67-68 Mustang doesn't have a clock, there's no loss there. Remove the cross-hair plate and install Retrogauge's Mini-Tach. If a clock isn't as important to you as a tachometer, pull the clock and put it away for safekeeping - or pass it along to a buddy doing a concours restoration who would like to have a factory clock.
Mini-Tach installs without cutting or special modifications. All you need is switched power (red - ignition on) and a lead from the negative side (green) of your engine's ignition coil. Two tachs, 0-6000rpm or 0-8000rpm, are available with faces that match 1967-68 Mustang instrumentation.