WARNING: This page is about a different car, the 2004 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.
Measure the tachometer resistance.
Fig 1: Measuring Tachometer Resistance
Courtesy of SUBARU OF AMERICA, INC.
Fig 2: Terminal Resistance Chart
Courtesy of SUBARU OF AMERICA, INC.
If NG, replace the speedometer and tachometer assembly.
If OK, replace the combination meter printed circuit.