tachometer problem

[GFC Jim]

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?

 

[ezmobee]

Sounds to me like the positive and the pulse wires are swapped somewheres along the way.

 

[GA_Boater]

Welcome aboard.

You are using the meter on a DC volt scale, aren't you. The voltage is AC. Also the switch should be on 6, not 4C. 4C is for a 4 cylinder. but not an outboard, rather an auto/truck based motor. Your tach is reading higher than the actual RPM's.

A snip from a Teleflex document;

 

[GFC Jim]

I have moved the selector switch to 6 and I am getting low voltage on the send post with the volt meter on an a.c. reading and the motor running at idle.The tachometer is still spinning all the way around past 6k so I think I can conclude that the tachometer is bad and not the rectifier

 

[GA_Boater]

The following has the voltage readings;