Review on Mini Voltmeter + Ammeter in case DC 0-100V 10A (red+blue) by Jnis Zels ᠌

No instructions come with the device. You will have to search to find the wiring diagram. First, as a rule, they find the wrong one, according to which the power of the device (indicator) is taken directly from the incoming voltage. If your input voltage is less than 20V, then the device will work, if more, it will burn out. In the case of a large input voltage, the device must be powered from a separate source. But the seller is silent about this.