If you need links to the Stator Papers and such, here's an excerpt from your mega-welcome.....
Perhaps you've already seen these, but I like to remind all the new members. In addition to the carb rebuild series, I recommend visiting the In The Garage section via the GSR Homepage and check out the Stator Papers. There's also a lot of great information in the Old Q&A section. I have some documentation on my little BikeCliff website to help get you familiar with doing routine maintenance tasks (note that it is 850G-specific but many tasks are common to all GS bikes). Other "user contributed" informational sites include those of Mr. bwringer, Mr. tfb and Mr. robertbarr. And if your bike uses shims for valve adjustments, send an email to Mr. Steve requesting a copy of his Excel spreadsheet that helps you keep track of clearances, shim sizes and other service work.
The Stator Papers will help you diagnose your charging system. Start with a known, good, fully charged battery then go through the tests to see if you have a bad stator or regulator/rectifier. First, it's a good idea to clean every electrical connection and ground on the entire bike, from headlight bucket to tail light including the fusebox. Run the ground wire from your regulator/rectifier directly to the negative terminal of the battery. This will correct the insufficient ground to the battery box that is standard on most of the GS models. Keep us informed.
Thank you for your indulgence,
BassCliff
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