Soon after I got my bike, I was looking at the wiring diagram and noticed it included an audible turn signal - ie, a warning beeper to let you know your turn indicator is flashing. I was very pleased, because it's really dangerous riding in traffic with your turn indicator flashing because you forgot to cancel it.
However, I had noticed no beeper on my bike. So I had a poke around about the steering head, and sure enough, I found two wires (or was three? I can't remember) doing nothing. I went and bought a beeper, A GOOD LOUD ONE, wired it in, and sure enough, it beeped in time with the indicators. Maybe you can do the same, if your beeper is missing. If I can do it, it must be easy. As Jon Slocum will tell you.
You can aim the beeper into the wind shield, which makes it louder. Mine is loud enough to hear at motorway speeds. Even with my bad hearing (too many drugs and loud motorcycles, and I worked for a while as manager of a rock group)