All my lights are working, but they won't flash on the left side. they come on fine with the signal switch no flashy, where do I start looking. I've already changed the all the taillights .

Have you checked the front bulbs? If one of them is bad, they signals will not flash.
Make sure you have the correct bulbs in them, too.

Try pushing on the bulb. I had a similar problem on my white 79. The metal part inside the socket that the bulb twists into seemed to not be making good contact with the wiring. After firmly pushing it in and putting the bulb back in it worked correctly again.

You can also try switching the bulbs around to see if the problem follows the bulbs or not.

Figured it out, the wire in the bulb socket, the one thats alone was loose. Took it out and bent it a little put it back in and it works great. thanks for the tips, Ric.