The problem I'm trying to solve: I have a vehicle that has 3 wires for the tail/brake light. When the vehicle is on there is 12v+ between the red and black wires and there is 7v+ between the red and Orange wires. When you hit the brakes the 7v+ between the red and orange wires steps up to 10v+.
So I need to create a circuit that will turn on a set of LED lights when the voltage goes above 9 volts. Currently, my circuit consists of a voltage divider (changing 12v down to 9v), an LM324N OPAMP and an FQI50N06 MOSFET (Schematic shows IRF540). For some reason, on the OPAMP, when there is no input, the output is on, when the non-inverting input is higher than the inverting input the output is on and when the inverting input is higher than the non inverting input the output is off. So in my mind, this circuit is working, except when there is no input, the the output should be off.
EDIT: Something that just popped into my head as soon as I posted this, I wonder if putting a diode on the output would prevent the output from being on when there is no input.
Please see the attached schematic:]1