Join Date: Sep 2006
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Re: Help figuring out this engine buzzer circuit
What you describe is perfectly normal.
Your 12V supply earths through the oil pressure switch.
When the engine is stopped, the oil pressure switch is closed and when you first turn the key, there is a circuit path through the alarm and through the closed switch.
When the engine starts, the oil pressure pushes the oil pressure switch open and opens the circuit to kill the alarm.