Interesting Tachometer Issue

[NCSUmoomba]

I noticed something odd with my tachometer this past weekend. The "analog" tach in the dash was reading about 500 rpm higher than the "digital" tach built into Perfect Pass. I think the PP one is right based on the speed we were going. What would make the other one read incorrectly? How does it get its signal?

[bergermaister]

500 seems like a lot. I have noticed mine off around 150-200 from PP at times but just chocked it up to newer/better technology.

Usually gets its signal from the (-) of your ignition coil. Maybe a lose wire somewhere? On newer boats I'm guessing it would be from the ECU.

[zabooda]

Mine moves around and I tap the glass until I get the rpm I like.