I decided to build a simple water/methanol injection system for my car and now I'm thinking about a simple way to activate the water pump only from certain boost level. For the boost reading I'm planning to use map sensor. The map sensor has +12v supply, ground and output pin (5v max). The output voltage varies depending on the boost pressure.
What would be the easiest way to activate a relay which turns on the pump when certain voltage (or more) is received at the output from the map sensor? Ideally with a potentiometer for the boost level adjustment but that would be just a nice to have option.