Problem solved - tach is pinning

[Pete Ambrose2]

I have a 2001 P T175 bass tracker with a Mercury 40 hp. As soon as I turn the Ignition to the on position the tac will move to zero. Once it is started, the needle will spin clockwise until the needle points to bottom and stays there even when shut off. Once I start it agan the tac will continue clockwise to the 0 position unti started then pin again. Where should I start?

 

[Pete Ambrose2]

rotated the selector dial on the back several times.