Factory tach reads 3500 rpm when engine is off?

[Sonny]

Ever since installing it, when I cut the key off the tach reads 3,500 rpm. Ignition on, goes to zero, engine running it’s accurate. Any ideas why? Bought it new aftermarket.

 

[HEMI-ITIS]

Because of what is involved to remove it and you verified that it is correct,,,,I would just leave it. Otherwise you have to send it back for recalibration or replacement.

 

[Kowal]

I used to work with the Sun Tach engineers, they were part of the business I was in. Their reissued old school tachs dropped the needle to 6 o’clock when not powered. It was the circuitry and built in logic, the tachs are completely micro-electronic versus more analog driven, it was just the way it was designed. When the tach is powered up, it immediately zero’d.

 

[beanhead]

Most aftermarket electrical tachs don't reset to zero without power applied..if you decide it bugs you too much, when you shut down just pause in the accessory position for a moment before turning the key all the way off.