The problem is almost certainly one of the below:
-Battery
-Rectifier
-Regulator
-Field coil
-Stator coil (unlikely, unless used as a road skid plate)
-Interconnect wiring
One method of repair is to guess and replace each or all of the components to affect restoration.
The other is to test some things with a voltmeter and/or ohmmeter, in order to determine which of the components are faulty. There will be some learning associated with this approach.
Which method is more suitable to you? Do you have any skill or knowledge of a multimeter? Have a multimeter?
Have you glanced at the FAQ yet?
Cheers,
