Pretty much any aftermarket electric/analog tach will be of the "-" terminal on the coil signal type. Some stock tachs in various vehicles (Smiths and Jaeger were famous for this) use the induction coil mentioned. In this case your hot lead to the "+" terminal at the coil goes through an induction loop in or on the tach on its way to the coil from the ignition switch. Oh, don't get the induction loop backward if you do use this type as it will permanently damage the tach.

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Mike!