I have a teleflex analog tach 6k with a 2002 mercury 115 4 stroke. when I start the motor the tach spins all the way around to the right past the 6k mark. I have cleaned all the connections on the tach and made sure the dial is pointing to 4c. when I turn the ignition on the grey wire attached to send is showing 12 volts, when I crank the motor I lose all voltage on the grey wire. I thought it might be the rectifier but the battery is charging according to the volt meter. I don't want to just start replacing parts that may be good. Any thoughts on what would cause the loss of signal to the tach when the motor is started?