Combination Meter: Tachometer
WARNING: This page is about a different car, the 2004 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
The tachometer drive circuit is connected to the engine speed sensing circuit in the engine control module.
When the engine speed increases or decreases, the voltage of the circuit also increases or decreases, changing the magnetic force of the tachometer drive coil.
The tachometer needle then moves in accordance with change in the engine speed.