If you're planning on using one of Auto Meter's awesome tachometers on an engine application without a distributor, then you're going to need one of these little guys. All of Auto Meter's tachometer's work by measuring the electrical signals caused by the distributor. Since the vast majority of modern engines use other ignition methods, its necessary to convert your ignition system's electrical output into a 12V current that Auto Meter's tachometers can read.
This adapter mounts in your engine bay and has polyurethane potted circuits to protect it from engine bay conditions. The adapter works with a huge assortment of engine ignition types, but may require different wiring for each application.