2003 Sierra left blinker problem

Hi -

When I operate the left turn signal (only the left, never the right), one of the following happens:

1. Blinker operates normally (I'd guess 10-15% of the time at this point)
2. Blinker "sticks," nothing happens - no noise, no lights.
3. Blinker "sticks," light comes on and stays on, there is no noise, and it does not flash.
4. Blinker comes on and shuts off the cruise control if CC is in use.
5. Blinker comes on, and at the same time both brake lights flash.
6. Blinker comes on, flashes for up to 10 times, then abruptly stops, even though I haven't turned or shut it off.

Any help appreciated.