1. Dirty or corroded battery terminals: If the battery terminals are dirty or corroded, it can prevent the battery from receiving power from the generator. Make sure the battery terminals are clean and free of corrosion.
2. Loose or damaged wiring: The wiring that connects the generator to the battery and regulator can become loose or damaged over time. This can also prevent the battery from receiving power from the generator. Make sure all the wiring is securely connected and in good condition.
3. Bad ground connection: The generator needs to be properly grounded in order to work properly. Make sure the generator is securely mounted to the frame of the motorcycle and that the ground wire is properly connected.
4. Faulty voltage regulator: Even though you mentioned that the regulator is working, it's still worth double-checking. A faulty voltage regulator can prevent the battery from receiving the proper amount of voltage from the generator. Test the voltage regulator with a multimeter to make sure it is working properly.
If you have checked all of these things and the Sportster is still not charging, you may need to take it to a qualified mechanic for further diagnosis and repair.
