ignition switch buzzer

[Gaylord Ballard]

I know its a dumb question but what does the buzzer mean on my ignition switch? I have a 34 Perkins. Sometimes it comes back on when the engine is running.

 

[Airstream345]

The buzzer is sort of like the "idiot light" on your car. It's wired into a "yes/no" switch for engine oil, engine temp or both. The intent is to tell you something is wrong (low oil pressure and/or high engine temp).

If it's going off underway then something is wrong (low oil pressure, high temp, false positive due to faulty switch/wiring).

Definitely something to get to the bottom of ASAP.

 

[Gaylord Ballard]

That makes sense. It buzzes when I turn on the switch and then about half buzzes after the engine has started. Not time enough to heat up and dash gauge shows plenty of oil pressure. Leads me to believe a faulty buzzer. I was hoping to find out what the exact function of it was so I can eliminate the trouble of tracing down multiple sending units/wiring problems.

 

[Gaylord Ballard]

Thanks

 

[Gdavid]

The sending units function as switches that close and complete the circuit to the engine block and become a ground when an undesirable condition is met like low oil pressure, high temperature, etc. There is 12 volts supplied from the keyed switch to one connector on the buzzer and another lead runs to the engine and then splits to the various sending units that are wired in parallel. If any of the sensors is failing in the closed position the buzzer will go off or if the wiring is chaffed and coming into contact with a grounded wire at any point, the buzzer will sound. I believe the perkins were wired to a temperature sending unit and oil pressure sensor originally but due to the age of these boats other items may have been added or removed from the circuitry. Disconnecting one at a time will find the fault or in the worst case, tracing the wire will find your short. For twin engine applications or boats with really quiet exhausts the buzzers are very useful in letting you know when an engine has stalled out before you go charging up to a dock with misplaced bravado.