Motorcycle Questions? Ask a Mechanic.
It sounds like you may have a bulb wattage issue. Has any of the bulbs been recently changed?
The system works when a minimum amount of amperage is drawn from the flasher module. If a bulb with too low a wattage is installed the flasher module will not create the flash. It is a common problem when LED bulbs are used but not too common when standard incandescent bulbs are used.
If you have correct stock replacement bulbs installed then you may have a grounding issue on that left bulb. There wasn't a dedicated ground wire on your year bike and the system relied on good contact being made through the mount and handlebars or fender depending on whether the problem is on the front or rear. You can check this by temporarily clipping a jumper wire from a good ground to the light housing and trying the signal. If this causes it to flash properly then the ground is your issue.
I hope this helps. Please let me know if I can be of further assistance. Also, please leave a positive rating for my service today. Thanks, P.J.