You should be able to reverse the wiring in the tail to check to make sure the LH turn signal actually works and isnt open or shorted. You can probably do that on the front, and the connectors should be behind the flyscreen. The result you are looking for is to see that when you flick the switch to the right, the LEFT signals should illuminate. This will ensure they are working properly. If they do, I would be looking into the switch or wiring on the turn signal.