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Square Wave Signal Hook Up

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12:00 p.m.: The Atomic EFI does not require an aftermarket ignition, sort of. What it does require is a square wave tach signal. While this is a common form of tach output on late-model vehicles, most vehicles that will be converting from a carb to EFI won’t have this. Hooking up the tach input to the negative side of a coil or to the tach terminal of a GM HEI won’t work. Most aftermarket ignition systems provide a square wave tach signal, and all MSD ignition systems do. We don’t need an ignition box for this application, so the simple fix was to replace the original HEI module with an MSD module (part #83647) that produces the square wave. We are sure that we’re getting better ignition performance now, as well.