A short tail about the electrical trouble I’ve recently experienced with my GS500.

It started with a flickering neutral light. It was fine at high revs, but on tick over there was a definite flicker. I whipped the seat off to find a battery terminal with a serious case of corrosion. Ahh, thought I. This is the problem. Cleaned that up and started the bike, still some flickering of the neutral light. Perhaps it’s always done that and I’ve just not taken much notice, everything else seems to be okay. I’ll just ride it. And so I did, right up until the thing died on me mid ride.
I coasted to a stop to survey the situation. With the ignition on, no lights etc. Nothing. I thought it was fully dead. Just out of curiosity I pressed the starter button and blow me if it didn’t fire up. I decided to ride back home and see if I could find out just what was going on…
Popped the seat off to find that the negative battery terminal was corroded again. Had a little Google search about this, which said that undercharging of the battery could cause it. Checked the voltage output from the reg / rec as per the manual. It was a little low, but then I knew it had always been a little low from previous measurements taken years ago. Tried a spare reg / rec that I had - same result, so probably not that at fault. Checked output from alternator. Again a little low, but also again the same as I had seen from previous measurements years ago, so unlikely to be the culprit. But, as I have spare alternator windings, I’ll give them a go. Removed the cover / alternator windings to find that one of the magnets was loose. Luckily I also had a spare rotor, so I’ll swap that too. Did all that. Made absolutely no difference to the voltage I was reading at the battery!
On a whim, I decided to check the main fuse. This wasn’t blown, but the corrosion on the contacts was severe and you could see that things had been getting hot at times. A new fuse didn’t solve the issue, as the contacts in it’s mounting block were corroded too, so a new unit was purchased. Now, with this fitted, I’ve never had so much voltage at the battery. It actually meets the specs in the manual!
Hopefully, then, that’s the issue sorted.
I should also note that when I removed the old rotor, the starter clutch bolts were also loose (another GS500 foible). They’re nice and tight on the one I put in!