All those lights you mention go thru the turn signal switch, sounds weird, but they do. I've read there can be feedback from bad grounds that could cause lights to flash, but not sure I believe that. A bad flasher should not cause both sides to flash, it is controlled by the signal switch. Your
turn signal switch would be my first guess as being the culprit. Provided it's not wired wrong.
If by flashing you mean they all are flashing in time with the flasher that you can hear, you will have to use a test light to see why the flasher is linked to all lights on left turn. The test light will blink right along with the rest and you can possibly follow the flashing lights! Also, if there is an
emergency flasher involved, that is suspect.
