My left turn signal started blinking really fast. I assumed that meant I had a burnt out bulb, but I checked both front and rear lights and they're fine, except that the rear one doesn't blink. I'm guessing that I have one of two possible problems:

1. The rear bulb is on its way out and isn't generating enough wattage to operate the flasher.
2. The switch is dirty or defective.

So my question is this: do these seem like reasonable possibilities, and if #2, where exactly is the switch so I can get at it?