Verify all your connections are clean and tight on the backside of th tach. The purple wire will go to the "I" (ign.) post, the gray wire to the signal post ("S") and the black wire to the ground post ("G"). Make sure the eng. harness to dash connector on the back starboard side of the motor is tight and free of corrosion (green stuff). Check the connections at the coil and make sure they are tight and free of debris. If this all looks good, contact your dealer or the parts "Guru", Anthony Cooper at Skiers Choice for price and availability on a new tach. Anthony can be contacted: email-
[email protected], or (865)983-9924ext.118. Hope this helps, keep us posted. Brian Raymond