Possible causes:
Flasher, ignition switch or ignition switch wiring, multifunction/turn signal switch.
The flasher is not mounted on the front of the fuse panel. The flasher on the front of the fuse panel is a separate one for the hazard lights. The turn signal flasher is in one of several places, depending on when your car was made. Some are behind the fuse panel on the back side, others are behind the radio and some are behind the glove box.
Other possible problem sources for the turn signal malfunction are the ignition switch, multifunction switch and the plastic shell that holds the turn signal wiring connector pins.
Cars with ignition switch or ignition switch wiring problems tend to have other things that don't work correctly or are intermittent like the radio, heater or windshield wipers.
A word of caution about multifunction switches is in order here. The multifunction switch (high/low beam, wiper, turn signals) are different for different years. 87-98 will work in any 87-89 car. The 90-93 switches only work in 90-93 cars. You can't put an early model switch in a late model car, nor can you put a late model switch in an early car.
Supposedly you can move the pins around to make the switches work in model years that are different from the car the switch came out of. I cannot verify that and haven’t tried it .