You'll need an isolated DC to DC converter to power the meter, or something like this that can measure its own voltage: http://www.amazon.com/Digital-Voltage-Panel-Voltmeter-7-5V-20V/dp/B005UWD2J4/ref=sr_1_2?ie=UTF8&qid=1391023520&sr=8-2&keywords=digital+voltmeter You could also find something on fleabay. Dave - AC2GL