Directional signals

Mechanic put in new flasher after problem developed; one side was blinking fast and the other side not working. I do not know if he changed any fuses or bulbs.
Signals worked fine when I picked up car. When it got darker I put on car lights then went to make a left turn, uh-oh no directional signal. Put right signal it worked. Turned off lights and voila, -right/left signals worked again.
Does it sound as simple as a bulb on the left side?