I'm having an intermittent problem with my speedo. It works half of the time, but when it's not working like it should it works more like a tach. I can put the truck in neutral at any speed and rev the motor and the speedo goes up and down like a tach. I have replaced the wires all the way from the speed sensor to the top of the engine, but I haven't gone any farther than that. Has any body else experienced this and found the solution? Or do I have to just chase this through the whole wiring harness?

 

That's pretty wild.

It's just a hunch but I would check the cluster ground.

 

Sounds like a wire shorting in the cluster.

 

mine dose this too wheres the cluster ground

 

Somewhat of a common problem as I have a 90 that moves the odometer if I rev it while it's parked.

 

On the back of the instrument cluster.

 

Thanks for the info. I was thinking this might be a ground problem cuz the temp gauge jumps when I hit bumps but I didn't know about a cluster ground.