Left Turn Signal Blinker Flashing Super Fast and No Left Headlights!

Did you plug everything back when you put the headlight back?

 

So now you go back and look at your headlight I'm assuming this is halogen headlights and you didn't have to remove the whole lamp assembly from the automobile or were able to just reach around and do whatever take care of the business so you left something unplugged almost guaranteed or you pulled something loose when pulling your hand out from around there something very simple and can almost bet on it nothing serious is just happen sitting there other than you pulling something loose or similar this model is not known for just things happening per se.

 

Sounds like headlight connector issue. Sounds like either one was forgotten or is fitted without being fully engaged.

 

On most cars a fast blink indicator on the dash when a turn signal is on indicates a burnt out bulb. (Going back at least 30 years.) The car cannot distinguish between a bulb which is open (blown filament) and a bulb which is not plugged in. Since the headlight is also out, and you just worked on that area, either a connector was left dangling or it isn't plugged in fully.