[Bob Lincoln]

Is it reading zero, or stuck, or erratic?

The tachometer is driven by a small 'daughter' card that plugs into the main circuit board behind the instruments. It might have come loose, or just have failed. It's a poor design that draws battery power with the engine off. I rewired it to run off the ignition only.

 

[Mred]

The tach failed in the full scale position. The needle stays in the full scale position no matter whether key off or on, and/or running.

thx

 

[Bob Lincoln]

That sounds like a stuck needle. I'd pull the instrument panel and flick it back to zero.