Turn Signal

I changed out my headlight assembly recently and
after that all of my lights work except for the left
blinker. When I turn the lights on it will light up
yellow, as it should but it doesn't blink when I turn
the turn signal on, but my rear blinker does and the
entire passenger side works perfectly, I don't know
if it is a bad ground, it shouldn't be the positive, as
it is getting voltage, but I can find the meaning for
the three wires "A, B, and G" I know one is positive,
and one is ground, but I can't tell which one is
positive and what the a and b is for.