A. Thanks To Stephan for sending this to us!
My í82 XV920 has been failing to charge the battery adequately and I finally solved the problem.
I would charge the battery fully on the bench, reinstall it, and have problems later because the charging system only appeared to put out 11.5 volts (far below the recommended 14 volts one expects) and the battery would run down again. I even replaced the four year old battery, thinking it might no longer accept a charge. No improvement.
I installed a voltage gauge on the bike to monitor this behavior and that confirmed it, the system was never charging more that 11.75 volts regardless of engine speed.
Following the Yamaha manual I tested every component I could find and cleaned all the connectors in the system. The last connector and the most difficult to reach was the one that connects the voltage regulator/rectifier (mounted down low between the engine sump and the rear head pipe) to the battery harness. You can see this connector through the triangular hole in the right foot peg bracket. You can even touch it with a fingertip, but you canít reach it to work on it.
Head on the ground, looking up between the frame and the battery, I was able to see that the red wire (of the six wires leading into the connector) showed signs of corrosion. To get to it, I had to remove the battery and its triangular bracket which is also the support for the battery tray, rear brake lever and brake light switch, brake rod, rear sub-frame, starter solenoid, two pegs and numerous electrical connections.
With all this out of the way, it was easy to pull the connector apart and see that the male and female terminals on the red wire were severely corroded. I replaced these two parts, cleaned everything else, used Boeshield spray to help prevent corrosion, wrapped the connector in a protective plastic sheath and reassembled everything. Upon startup, the gauge showed 12.5 volts at idle, rising to 14 volts at 2,500 RPM. Success!
Incidentally, some years ago I had bought a spare regulator off a wrecked bike and the connector on the spare shows the same signs of corrosion. This leads me to think the problem is not limited to my bike alone. If yours exhibits charging problems, I suggest trying this solution before spending money on expensive electrical parts you may not need.