What would cause the turn signal indicator light in the dash to blink really fast?

 

Check for a blown bulb.

 

They also blink fast if there is too much load such as a trailer or short to ground.
What I've run into a couple of times is a trailer jack full of dirt. When it gets wet it can short out. Not enough to blow the fuse but enough to make the signals blink fast.

 

I can remember which way it works fast or slow but i do know there is a different flasher for a heavy duty and there is standard. The standard will not work if you got a trailer hooked up but i cant recall if it blinks faster or slower.

 

Heavy duty flashers flash faster than normal until a trailer is hooked up and the current load is increased. At this time, the flashing slows down to normal.
A fast flasher is the indication of a burnt out bulb, decreasing the load on the flasher and therefore flashing faster.