Re: OMC Tach ???
It is easiest to check for 12-volt power and proper ground first. A volt-ohmmeter or 12-volt test light are great tools for this procedure. Simply ground the meter or light, turn the key on and touch the positive probe to the purple wire on the back of the tach. You should see 12 volts indicated on the meter, or if you?re using a test light, its bulb should illuminate. Reverse the leads to check for proper ground, or use the ground wire on the tach to ground your meter or test light.
If either the power circuit or ground is the culprit, you can repair the problem and the tach should work fine. In a no-power situation, see if your tach has an inline fuse. These often blow due to constant vibration. After inspecting for power and ground, if it still doesn?t work, it?s time to check the signal-input source, or the tach itself.
A simple way to determine if the tach is bad is to use another tach. Some shops will have a tach ready with alligator clips just for this, ask them and see if they will let you borrow it, or borrow one off a buddy.
In the event you don?t have access to a shop tach, you?ll have to refer to the manual to check the signal source. The signal is a pulse-positive output that?s provided directly from the stator assembly through the rectifier. A peak-reading voltmeter set to ?positive? and the lowest volt scale will enable you to read any voltage output (on this circuit) from the stator.
Check the procedure and specifications for your engine, since the inspection point, procedure and wiring are not the same for all outboards. In addition, your ohmmeter can be used to check the continuity of the stator windings, as well as the integrity of the rectifier diodes.
If everything still checks out, you will need to test your rectifier/regulator as per your Ezeke's instructions. The following links will help with troubleshooting this.
http://ww2.tflx.com/pdf/obtach~1.pdf
http://ww2.tflx.com/PDF/99320.pdf
