Recently my turn signal flashing has been erratic. I don't simply mean the sort of hyper blinking that you see when a bulb is out. Valerie checked every bulb (side markers included) and confirmed they all work. But I've been seeing combinations of steady light, no flashing, changing speeds, etc. I saw the same thing when I pressed the hazard light switch as well. Since all my bulbs worked, but the flashing was failing, I figured it a relay, not a fuze. A relay is basically switch controlled by electricity, and in this case it cases the lights to flash.
In the case of my 2004 Jetta I was lucky. As it happens, the flasher relay is combined with the hazard light switch. After some research, I read online that it's easy and low-risk to pop out of the dashboard. I found a replacement part on Amazon for just over $12 after tax, and today it arrived. The hazard switch indeed popped out with ease and, after attaching the new one, it worked flawlessly for both hazard lights and turn signals in both directions. I've been very happy with my mechanic for many years, but I probably saved myself around a hundred bucks on this fix. I'm not the handiest fellow, but it's immensely satisfying to fix something like this on my own.