The buzzer wire is positively charged by the ignition wire, it runs to the oil
pressure switch on the engine
near the forward end. When the ignition is turned on, and the engine is not running (i.e., not creating oil pressure), the switch is the ground. When the engine is running, the switch turns off, shutting off the ground to the oil pressure buzzer. The toggle switch is a separate connection to ground, making the buzzer go off. Sounds like the oil pressure switch might be faulty.
If you install a tee where the switch is located, you can add an oil pressure sender to allow you to read the actual oil pressure. I mounted a red alarm
lamp above the oil pressure gauge, in parallel with the buzzer. That way anybody can understand that the noise
is oil pressure related.
While I was at it, I added additional idiot lights and buzzers to let me know when the engine was overheating
, when the waterpump stopped doing so, when the fuel filter
vacuum got too high, when the alternator
stopped making juice, when there was water
in the fuel filter
, and when the regulator
had been switched into small engine mode. Each buzzer was a different sound (Radio Shack sells them) so I can be asleep, offwatch, and know what alarm
just went off.