The tachometer operates off of the engine's charging system. It is possible that either the stator, or more likely the rectifier, is failing. Check the rectifier out as follows.

********************
(Small Rectifier Description & Location)
(J. Reeves)

On most 2,3,4,6 cylinder engines, the small rectifier is located on the starboard (right) side of the engine just in front of the engines electrical wiring strip. There are a few older V4 engines that have the wiring strip on the rear portion of the engine and the rectifier would be located just under that terminal strip. The smaller horsepower engines usually have the rectifier located on the starboard side of the powerhead close to the carburetor area.

The rectifier appears to be a round object approximately one inch (1") in diameter and also about one inch (1") high. The base of it is sort of triangular in appearance and is attached to the engine with two (2) screws/bolts..... usually one screw/bolt is larger than the other. The rectifier, depending on which one your engine uses, will have either:

One Red wire, one Yellow wire, and one Yellow/Gray wire, or One Red wire, and two Yellow wires.

Note that either of the above rectifiers could have a fourth wire which would be Yellow/Blue
********************
(Small Rectifier Test)
(J. Reeves)

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 a$$y immediately.

Will this cause the alarm to stay on? I changed the Rectifier last week and it worked fine.

I a$$ume that you're saying that the tachometer now works fine. No, that shouldn't be affecting the warning horn.

With the horn sounding (Key ON - Engine NOT running), remove the TAN wire from the horn. If the horn continues to sound, the horn itself is faulty.

If the horn stops sounding the instant you remove that TAN wire, either that wire is grounded out somewhere OR a sensor at the engine is faulty (grounded).

Thanks for the info. It appears the horn is faulty. The tan wire makes no change either plugged in or unplugged. I unhooked the purple wire and it goes off.

I'll order a new horn and see what happens.

Thanks, you were great help.
Chester Ables