2006 Siverado, Left turn signal works occasionally
 

My left turn signal works occasionally. Usually in a specific outside temperature range. My right works fine. I have replaced the left harness and lens. Also replaced the connector block that connects both signals. My thinking is it's a short or faulty ground that only affects the left side, somewhere from the rear electrical block forward. I also replaced all bulbs. It does work sometimes when it wants to. Does anybody have any suggestions a to where to look? I am limited on electrical experience and therefore I would not know what I am looking at on a schematic. Thanks in advance.