How to make a warning buzzer circuit for an oil pressure gauge on a car

I am installing an aftermarket oil pressure gauge made my Autometer in my car. The gauge uses a sending unit that uses resistance to send the pressure reading to the gauge. I was wondering if there is any way to build a circuit to make a warning buzzer go off when the oil pressure becomes too low. Please let me know if this is possible, and also let me know what information on the gauge you need to know to help me make this circuit.

 

The sending unit you have puts out a variable resistance for the gauge, not what you need for a buzzer. If your vehicle originally had a oil light the sending unit for that was basically on/off. You could put a 'tee' at the motor,put the gauge sending unit in one side and a sending unit for a light on the other side. The unit for the light will connect the terminal to ground when pressure is low (about 10 psi I think) . You then could wire the positive of the buzzer to a source that is hot with key on and the negative to the sending unit. What it boils down to is, you are switching both positive and negative of the buzzer.

EDIT: you might be able to tap into the signal from the gauge sending unit, but it might affect the true value of the oil pressure.

 

Well, need a bit more information.

What voltage do you read at the pressure sender unit with the engine off, ignition on?
What voltage do you read at the pressure sender unit with the engine running, normal oil pressure?