Low Battery Issue

I recently picked up an '82 Seca 750, my first road bike, and I'm having a problem with the electrical system. The Low Battery light on the bike comes on nearly every time I ride it, turning off only when I'm running at speed and near peak alternator output (4500 - 5500 RPM).

I replaced the battery when I got the bike 2 months ago with the thought that it was likely the culprit, but the problem hasn't gone away. At this point I'm assuming it's an alternator issue, but I'm not familiar with the way that works on a bike compared to a car. It seems there's multiple parts I can replace, and I'm not sure which is the likely culprit.

Thoughts?

 

Measure your alternator brushes first.

 

Look at the twin "Paths" on the Alternator Rotor that the two Brushes follow.

The Paths should be smooth and clean.
If there is any scorch marks from Brushes too short ... see if you can work-out the discoloration with this indispensable tool:

http://www.officedepot.com/a/products/9 ... erralID=NA

Use the GRAY side to "Dress" the Orbits.

 

at that age I'd be amazed the battery sensor works at all.

 

Militant the bike only had 10.5k on it when I bought it and is in near perfect shape, everything still runs on it.

I'll take a look at the alternator bushings, is there a standard I should be measuring them against?

 

10mm or less = Replace.