Turn signal problems

The left turn signal on my '89 is beginning to give me problems. From time to time (and more often of late), the left turn signal does not blink. Right turn signal, no problem. Left turn signal will work/blink most of the time, but not all. What is most likely the problem? I.e., where should I start? Thanks for any/all advice you can provide!

most likely it is a bulb. sometimes works and sometimes not. this is a common thing. change out the bulbs, then go from there.

Thanks CaledoniaBrian !