We can guess just like you did, but the results will be the same.
Got tools? Got skill? Lets try diagnosis of the problem before you go buy a bunch more stuff.
1) Charge the battery with a charger at least 5-10 amps for 16 hours. A Battery Tender is not a charger, and don't skip this step. Don't skip any of these steps.
2) Test the resting battery. Resting voltage should be above 12Vdc
3) Load test the battery. Load test the battery. If you don't have a legit load tester (cheap at harbor freight), crank it for 10 full seconds (by disconnecting the coils) and you should have more than 9.6V the whole time.
4) Test the draw from the battery. Disconnect the battery negative and put your DVOM (free from Harbor Freight with a coupon) one lead on the terminal, the other on the wire, set at amps. You should have less than .5A. Alternatively you can use a test light, (also free) and if it lights up you have a draw. Unplug the fuses until the meter drops or the light goes out. That is the circuit to check.
5) Test the charging system. Hook the coils back up and start it. You should have 14.3-14.8Vdc at 2500rpm. More than that and the VR is bad, less than that and the stator or wiring is bad.
I'm guessing 4
Post your results and please give some info about the bike.
Just bought it? miles? history? good condition? just started? Been going on for awhile? how long until it doesn't start? a day? a week? all winter? Is the battery new? who worked on it? Harley? your "car guy buddy"?
