I've noticed on the last couple of rides that the self cancelling turn signal switch on my 86 ZN1300 doesn't always self-cancel on the left side. I would say about 10% of the time, the left blinker will stay on while the right side self cancels 100% of the time. I remember having to take apart my 79 KZ1300 turn signal switch a few times to clean it out and make it operate smoothly - it would get quite 'sticky' - while the switch on my 86 works smoothly enough, just doesn't always cancel properly. Anyone else experience this behavior?
Let's not forget that the cancellation board needs to see 4 or 5 flashes of the light circuit + a 50 count of the speedo counter to cancel the signal SO, in its logic, if it doesn't SEE the resistance of the circuit, it won't initiate a cancellation phase. That being said, bad connections to the feed or ground in that circuit could also be an issue. Check the grounds at the signal lights and the wire terrminals on the ground and feed wiring as well. If I were troubleshooting this, I would start at the grounds for the signal lights themselves due to the exposure of them to the environment.
I can appreciate the supplied resource topic discussing the cancellation board and bad soldering as it's valuable info. I learned a hard lesson trying to troubleshoot a failed heated driver's seat in an Audi 5000 turbo quattro. The circuit involved 5 relays, 3 circuits and God knows how many switches. After 4 days of testing, I finally decided to resistance test the heating element in the seat ans sure enough it had an open circuit. In hindsight, I should have taken a moment and thought through just what most likely could break. Sitting in the seat, getting in and out of the seat, bouncing in the seat- why didn't i think it was the most likely failure.
Bottomline- Electrical troubles- grounds and connections, grounds and connections before anything else. The electrics on these bikes are subject to the weather you ride in. If they built these bikes with amp seal weather tite connectors then it might be a slightly different story. Bullet connectors are far from weather tite.