First and foremost, make sure there is a protective cover over the positive (+) terminal. This has been known to be the source of the problem on more than one occasion. With this not being covered, it's easy for a short to happen.
If it's covered, then this sounds like you may have either a bad stator (alternator), or possibly bad diode(s). Either one will prevent the battery from charging. To check the system, I recommend that you first check the battery's voltage to make sure it's fully charged. If not, charge the battery until it's fully charged. Next, if the lights are wired through the ignition, then with the key in the "on" position, turn on the headlights just long enough to check them. After that, with the negative terminal of the battery disconnected, and the ignition "off" and key removed, use the ohm's setting on your meter and check the diodes. Using the nearest points that will allow you to make a good connection with your meter, check to make sure that the electricity flows in only one direction. This is done by checking it one way, then reversing the leads and checking again. If you are using the continuity mode, you may hear a short "muffled" tone that will last for less than a second. This is normal. If there is no difference noticed when the leads are reversed, the diode(s) are bad and will need to be replaced. If these check out fine, then with the charging wires still disconnected, reconnect the battery and start the engine. With your volt meter set to the D.C. mode, Check the voltage at the battery connections. If it's the same as the battery, check the amount coming through the diode(s). If it's higher, you have a bad wire in the charging circuit. If this checks out fine but the problem remains, you more than likely have a weak battery.
