I have an LED (5mm, 2V 20mA) which is always on from a 12V supply. (I assume it has some resistors to drop the voltage.)
I need to turn this LED off when another power supply line gets a 3V input, and when the 3V is not there the LED has to stay on. What is the simplest circuit to achieve this? The input battery will be like a 12V 7.5A one. Please help.
An image of the current setup is as below.