A nice find at the recycle store, its a engine tach and not some sort of industrial tach?If its a "modern" tachometer, not requiring a separate sending unit like the old Suns, then you will find a wire for the ignition switch, a wire to go on distributer side of the coil, a ground and usually a wire for the illumination.Usually it does not make a difference if you hook up the power wire at the ignition switch or after the resister on the coil itself .Eliminate the wires one by one, the ground and illumination wires should be easy to figure out.Then you have only the 2 wires left for the switched power and the points. Hook it up briefly to see how if the tach works, it won't ruin the unit if the those two wires are crossed for a moment.
