when I use my left blinker,it also blinks the right blinker,right side works correctly. 2004 crew cab please help.

Have a look at at the left side bulbs to see if the filament has dropped and contacting the second filament in the bulb .

Check your trailer wiring for a short.

I agree with both, i have seen bulbs do that and the trailer plugs are known for corrosion which could cause the same concern. My money is on the bulb.

I bet that it is the flasher module. Failure of the flasher can cause all sorts of strange results.

flasher module. Mine just did this about two weeks ago, replaced flasher, problem fixed. Check out this post : http://www.dieselplace.com/forum/showthread.php?t=123607.

There is a new part # in that thread that i think updates the flasher with a better design. After I replaced it, the ticking sound is a little different. It's about $70 at the dealer, a little steep, better than being the multifuction lever though.