This low pressure switch is a great way to detect loss of coolant. It will turn on a warning light as soon as the coolant pressure drops below 3 psi. Temperature gauges do not react as quickly to coolant loss, and often show a cooler temperature because of the rush of cooling air! This switch is designed specifically for use with water and glycol-based coolant. Installs in a 1/8 NPT female port. Single-terminal grounding switch requires a 2-terminal warning light (such as any of our warning lights).