Autometer Stack Instruments 52mm 50-115 Celsius 3/8 BSPT (M) Mechanical Water Temp Gauge - BlackMechanical gauges do not require 12V power to operate. They make direct physical contact with the item they are reading. They do this through tubing or lines, which eliminates the need for electric signals. Installation Instructions Mechanical gauges do not require 12V power to operate. They make direct physical contact with the item they are reading. They do this through tubing or lines, which eliminates the need for electric signals. Ideal for