My right turn signal functions flawless. However, when I use my left signal, it doesn't blink. It just stays on solid. What could be the problem?

Try tapping the flasher. It's usually a round thingy in the fuse box that makes the distinctive clicking sound. Tap it a few times while the left blinker is on. Sometimes it will get stuck or corroded on the inside and tapping on it will fix it for a little while. I'm pretty sure you'll have to change it out anyways.

Also, check your bulbs. Put the right side into the left side and vice versa. If the problem moves, then it's your bulb. Some cars have that as a safety feature to let you know the bulbs or flasher aren't working properly.

This once happened to me. The problem was a short in the plug for the trailer lights (on the rear bumper).