An exhaust gas temperature gauge is powered by:

The exhaust gas temperature gauge is powered by a thermocouple, which generates its own voltage based on the temperature difference between two junctions of different metals. This principle is crucial in measuring high temperatures within engine exhaust systems. As the exhaust gases heat one junction, a voltage is generated, which is then translated into a temperature reading on the gauge.

This self-generating voltage feature of thermocouples eliminates the need for external power sources, making them ideal for applications like exhaust temperature measurement where reliability and accuracy are essential due to the harsh conditions. Other options suggesting fixed voltage supplies, such as 12v DC, 115v AC, or 28v DC, imply reliance on external power sources, which is not compatible with how thermocouples function in this context.