How do you test turn signal switch?

[rgunlock]

This is in a 78 GMC K15 with new AAW wiring harness and new turn signal switch (from Rockauto.com I believe). Right turn signal works fine. If I hit the lever for the left turn signal, I hear the flasher relay click about 3 times then the 10A fuse for the turn signals blows.

I've tried replacing the flasher relay module in the fuse panel but made no difference. I've removed all the bulbs from left front, side and rear and the fuse still blows after a second or so after pushing the turn signal lever to left turn.

Both turn signals have been working for the couple months that I've been driving the truck until one drive I noticed I have no turn signals - fuse is blown. Trying to narrow the problem down, the fuse blows every time after a couple seconds with the lever down for left turn signal.

So, all the wiring in the column is new, but I suppose I could have routed the wiring wrong within the column. Might be something besides the column entirely, but I've traced the wiring front and back and its all sitting snug in its conduit without any sign of wear or burns.

What else would you test? I've got a multimeter and amateur skills with it. Looking for anything to tell me whether the problem is likely in the column before I tear it apart.

Thanks --Rick

Edit: after starting this thread, I searched "test turn signal switch" and found this thread where ray_mcavoy describes testing the turn signal switch http://67-72chevytrucks.com/vboard/s...d.php?t=629205. This search worked much better than "left turn signal blows fuse". I'll be trying the tests he described.