you have a hot marker, hot signal, and a ground the ground is same left and right, the marker is also same color left and right, the signal wires are dif color left and right. now on a semi they will wire the pole lights on bumper to both hot wires to give a marker light that shorts (blinks) when turn signal is applied. most of us are opting for a signal light so connect to ground to black and left positive is red and right positive is green. that was looking behind light still connected so not 1000% positve. just check before you button everything up again to make sure all works well.