Hello group,<br /><br />I just bought a used tach on ebay. Its an OMC tach from the 70's. I have a 1975 Johnson 70hp. I set the tach on 6 at the back. I hooked it up to the terminal the manual for the motor said and have no reading on the tach at all. I checked the voltage at the 2 wires and I have 2-3 vac. Is this correct? The tach has 4 wires in the back...grey-purple-blue and black. I hooked the grey to the grey in the control. I hooked the black to ground. I tryed a ground on the motor and then on the mounting bolt on the control. Am I doing something wrong here or did I buy a dud tach? I believe the fellow when he said it worked when removed from his boat, but who knows. Any help I can get would be great.<br /><br />Best Regards<br />Arnie 