XCSOURCE DC 300V Voltmeter Ammeter Red Blue LED Panel Amp Digital Volt Gauge YB27VA TE72 The voltage between the thin red and thin black lines must be within DC 4.5-30V The ammeter can only be connected to the device under test 10A below ammeter (include 10A) with built-in shunt If you want to test the device above 10A, please remember connecting the external shunt when the black thin line vacant, it is better to use insulating tape around the exposed part of the wire, to prevent short circuits if just be used as a voltmeter, it is recommended that the yellow line and the black line were connected together, to prevent the ammeter digital flashing