Note voltage with yellow and red connected is40V.To measure greater than40V (up to 100V) the yellow wire is connected to a separate voltage source that is40V or less Voltmeters:Total 10PCS, 4 colors optional; 0.28 inch LED Panel; small in size and light in weight Features:Reverse polarity-protection, voltmeter will not burn out if reverse-polarity is applied; high-precision; low starting working voltage; fine function Good This product is materials, exquisite workmanship, very good and long service life 2 Connection Methods:3 wires are connected separately to measure voltage and power(yellow red is both forpos, black isneg); 3 wires are used as 2 wires, connected to measure voltage(Red and Yellow can be pair forpos, black isneg, Manufacturer: BOYANDM