I have a non working rev counter in my x type 2.5v6.
The needle just trembles on the lowest point and doesnt move with the engine speed.Have ssen gearbox speed sensors for sale online,would this be what i need and does anyone have a diagramme asbto where it fits so i can check my old one? Its a 5 speed manual

 

The rev counter is calculated by the ECU. So, having a quivering needle is telling me that you most likely have a bad instrument cluster since you don't mention a check engine light. The engine RPM is based off of the crankshaft speed sensor which also does the plug firing. So, if that sensor was bad, you would be getting a lot of error codes dealing with the engine. In this case, the engine would then go to the cam shaft sensors and figure out the engine rotation and get pretty close so you can get the car to a local service station.