I don't know about your 426 but the 450 has an ac circuit for the light and a d/c circuit for the battery.
To check the output of your stator use a multimeter set to ac, should be about 120v ac I think at the headlight connector. Check the service manual. If you don't get that at the light connector then meter the stator to see I you have the correct resistance then start the bike and see if you get the correct voltage. If the stator is good check the rectifier then the wiring harness for shorts to ground. There's no easy way to diagnose wiring problems. Break out the manual , meter and a cold beer and start learning.