Directional signal won't blink on one side

[IIA]

The directional signal/turn signal on the left side of my IIA won't flash/blink. The right side works normally and, when I turn the hazard lights, on all four blink normally. I replaced the flasher unit about a year ago. Any ideas what could be the problem?

[caperover]

Check your grounds.
I had a similar issue after removing the front wings, cleaning, painting, and reassembling.
After chasing things down with a volt/ohm meter, I finally ran a ground wire from the wing to the chassis and it fixed the lack of blinker problem.

[phartnady]

Had the same issue, removed the directional lens, noted that one screw holding the assembly had a copper piece that was corroded. Removed screw and used dremel to clean the copper piece, reassembled and worked great. Just my 2 cents. Best, phil