A tachometer built for a points-style ignition can read false spikes once you switch to a higher-energy ignition system, causing a jumpy or inaccurate needle. This OER tach filter conditions that signal so the gauge reads true again.

OER MG019219 Tachometer Filter Overview:

• Installs in-line between the tachometer and the ignition signal source
• Traps and dissipates the high-voltage spikes emitted by high-energy ignition systems
• Reshapes the signal into a steady square wave for accurate readings
• Compact 2 in. x 0.75 in. x 1 in. housing fits behind most dashes
• Fits 1967-1989 GM cars and trucks