They're usually pretty reliable. Worth checking the small white connector in the back of the tacho. Changing the lamps can sometimes pull on the loom and the connection itself isn't that positive. Try moving the connector with the engine running to see if the tacho stirs..........
They can be checked using a mathesis, but that's only really a techy way of wobbling the connector
Have you checked the two fuses up by the ECU? The tacho is fed from the Fi system, although if they go i think you'd have more than an inoperative tacho............ worth checking though.
Other than that, i'm guessing you shorted something to blow a headlight? could have took out the tacho pcb as well?