Once you get the turn signals working by fixing the flasher or the short. The next thing is to see where your brake light wires are touching. Turn on the left and right turn signals, do the parking lights flash too? With both directions? If it only flashes with one side then you have narrowed it down to which two wires are contacting each other. I had a similar problem and that is how I found it, it turned out there was two wires pinched together in that same 4-wire harness that runs to the tail lights. Then later on it happened again, I swore I fixed it right. Well this time it was a different problem, one of those "Hoppy" plug in trailer wiring connectors was shorting out inside of itself, cheap crap.
Good luck man.
