Originally, yes. When rebuilt/recalibrated with 2006 era electronics, usually 3 or in rare cases perhaps 4 wires (power, signal, ground and possibly illumination). This is partly because original tach wiring was in series with the ignition. If the tach quit, the engine quit. Usually upon rebuild the guts of the old tach are discarded and a new circuit board (or similar) is installed. This new circuitry requires the 3 or perhaps 4 wires. Hope this helps!
That's right. Two wires (signal and power), and the rebuilt units also always seem to need a separate ground wire. I grounded mine to the instrument column support behind the middle of the cluster. Ilumination is as all the other gauges are illuminated. If the unit being discussed is an externally mounted Sun type tach or hood mounted tach, then it will have an additional wire for its own illumination, but that's of course becuase being on a hood or dash lip (a la 66 Shelby) it needs its own illumination.