[patrickt]

Here's a simple test that I think will work. Pull the yellow wire off the flasher, and pull the two fast blow fuses out of the fixture behind the trailer relay. Then put one lead of a test light bulb on a known good 12v positive and the other lead on the yellow wire you removed from the flasher. Then jiggle and wiggle the turn signal on and off and see if you can get the bulb to light. If you can, then you know the switch is shorting out. Oh, and remove the front turn signal bulbs first.