As of 2010 the answer is no. It is recommended to use your turn signals when changing lanes, but not a law.
You could be hitting the flash feature on the turn signal arm when you use it.
It is more than necessary. It is required by law to use your indicator any time you change lanes or make a turn.
Bad flasher unit or turn signal switch
We could use a little more info here. The turn signal light? In front? In the rear? The turn signal switch?
Reason number one - it is a law. Reason number 2 - it allows other drivers, pedestrians, and cyclists to know what your intentions are.
Every time you turn left or right, or switch lanes on a highway you should use your turn signal in your car.
To effectively signal your turns while riding a bicycle, use hand signals and turn signals. Extend your left arm straight out to signal a left turn, and your right arm straight out to signal a right turn. You can also use a bicycle-mounted turn signal device for added visibility. Remember to always check for traffic before making your turn.
No.
Yes, it is illegal to not use a turn signal while driving in most places as it is a violation of traffic laws and can result in a citation or fine.
Bad bulb or crossed wires somewhere. If it only happens, say, when you use the left turn signal, but not when you use the right turn signal, it's probably one of the left-side bulbs.
In many cases, the brake light and the turn signal use the same bulb.
If you mean turn signal hand signals, then yes.