Right now, I'm held up by this instrument. The documentation speaks of THREE wires: Red, Black & White. On the back are FOUR wires: Red, Black, Yellow and Green. Red and Black are simple, +12 Volts & Ground. White is DIM as is Yellow, so that's not a big problem. Need to find out where that Green wire is supposed to go. E-mail off to Support@fdatasystems.com requesting the information.