My 1982 Yamaha XJ650 left turn signal was acting up, it wouldn't flash anymore, but the right turn signal was fine.
At first I thought my flasher died (I is 23 years old), so I went looking for a replacement. (Tip: Did you know that sometimes automotive flashers will work on motorcycles at 1/10th the price?) Unfortunately the automotive ones didn't work this time and I an OEM one is $66.
After a week I noticed my back left turn signal bulb died. So I purchased a new pair (always good to replace both). Tip: again, automotive bulbs will work fine at 1/2 the price.
After replacing the left turn signal bulb, the flasher started working again.

So, if you have problems with your flasher, don't forget about the $1 bulb, it maybe on it's way out or is rusty and causing problems with the flasher.

Mike.