Double check all battery connections, and have the battery tested. Pray it isn't the charging system. I learned that installing a new magneto/charging coil isn't a lot of fun:
What you see there is the easy part. The PITA is having to pull the new wiring up between the battery box and the air box. Even using the old wires to pull a 'fish' wire didn't help.
What you can't really see in the picture, is that the bike is up on a nice motorcycle jack.
If your battery and connections all check out, there is a simple ohm meter test for the charging coil described in the Clymer manual. It just involves unplugging a connector in the wiring harness and checking the resistance of the charging coil. If you need help with further diagnostics, just yell, and someone will help you figure it out.
Addendum: Continue to pray it isn't the charging system, I just priced the magneto pickup/charging coil (all one assembly) at Ron Ayer's and they go for the Princely sum of $241 + shipping! I lucked onto mine on eBay for $35