Why does my blinker blink really fast now? It just started out of the blue last month. Only driver side for left turn (not hazards)?

2005 Ford Freestyle

There's a fuse that needs to be replaced.

It is blinking fast because one of the bulbs are burnt out.

Because one of the bulbs on the left side is blown out.

That happens when a blinkers out

You have a bulb gone!

At least one of the filaments in the bulb is blown.

Most common would be a simple bulb failure ( or led set if fitted) the voltage supplied to the indicator unit ( small electrical box that cause power to switch on -off thus creating the blinking effect) ought to be stable and shared between a load e.g. 2 bulbs. Where one bulb fails, is disconnected. Wire broken etc the result is excess power ( volts ) is handled by the unit and effect is the rapid blinking due to working twice as fast as only half the load/ resistance on unit. Check bulbs first. Then connections.