"Here is a test that Joe reeve
"Here is a test that Joe reeves posted a long time ago that should cover your rectifier
Perhaps your engine does not have the water cooled regulator/rectifer but rather incorporates the smaller 3 wire rectifier which sits just forward of a vertical electrical strip on the starboard side of the engine.
If so, a failed rectifier would knock out the tachometer. See the following.
Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.
Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.
Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.
Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately."
