When you switch the left turn signal it doesn"t

Look Behind the triangle panel on the left side of the bike. Next to the battery. FUSES

Get a schematic for the car and clean and work every connection in the wiring to your switch. Also chemically clean the innards of your switch(s)

This is going to sound like a stupid question, but are you using the turn signal properly? The turn signals are on the left of the steering wheel and wiper controls are on the right side of the steering wheel on you car.

Sounds like its time for a turn signal switch. Something has come apart.

Try wiggling the switch around next time it doesn't work. It might be a poor connection in the swithch.

While a fast flash usually indicates a burned out bulb, you've obviously covered these bases. Your next step should be to check the turn signal solenoid, also called a turn signal "flasher", as these ususally cost between $6 and $12. If that doesn't fix your problem, you may be looking at a new turn signal switch (that's what they're called, even though they control the headlights, too.) Just make sure you exhaust all other options, as these cost around $270.

possibly flasher unit faulty
or turn signal switch

Both turn signals use the same fuse. If the left side signal works, you may have a burned out bulb on theright side, sometimes even a side marker bulb can cause the problem. Or the turn signal flasher could be worn out, but this usually effects both sides. A third problem could be the turn signal switch. The switch is located inside the steering column and does require some special tools to replace it.
rate it

signal switch replacement is a common issue, i've replaced 5 so far.