Erratic Tach

lately I have been getting erratic tach readings while in cruise flight. Can anyone suggest what may be causing this malady?
Roger

Roger, what type of engine monitoring system are you using? What type of aircraft and engine type?

Thanks Trevor,
I have a Van's RV6A with an AF2500, Lycoming 0360 A1A engine.
Roger

You might try removing, cleaning, and reseating the wires to the analog module. Also do the same for the splices that go to the RPM sensor. If that doesn't work, you may want to get a new RPM sensor and give that a try.

Thanks Trevor,
I'll let you know what happens.

It looks like I need a new RPM sensor. How do I order?
Thanks,
Roger

Trevor,
Thanks for the help. The problem turned out to be a bad connection under the cowl. The builder had used spade connectors instead of aircraft inline type and they had loosened up from vibration. Changed connectors and problem solved.
Roger