The speedometer turning on and off?

Hello,

It sounds like you might have a faulty vehicle speed sensor.
That sensor is located on top of the transmission (see diagram).
The speed sensor senses rotation of the transmission shaft and send that signal to the ECM and then the ECM send the information to the gauge cluster to display the vehicle speed.
Since your speedometer works on and off you might have a loose connection. Check the wires that goes to the sensor make sure it is connected securely and not corroded.
You can also test the connector to verify you are getting power to it.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://youtu.be/f3bETtCIdxM

I have attached diagrams for your reference.

Please let me know of any questions.

Thank you.