I know you havnt been reading and following the manual, because if you had, you would know that the black box is the CDI and not a regulator. The CDI rarely goes out, unless physical damage is noticed. Follow the manual, it gives you a trouble-shooting section for the electrical system. It comes in very hand most times I have used it. You may be forgetting somthing, so just read the manual. Good luck!
THE 80's RAGE! Currently owns:
81, 85 Yamaha Tri Moto 125
83 Yamaha Tri Moto 200 x2
82,83 Yamaha Tri Moto 175 project
85 Yamaha Tri Z 250
84 Kawasaki Tecate 250
84 Honda ATC 70
85 Honda ATC 350X
84 Honda ATC 250R
(2) 84 Honda ATC 200x
82, 83 Honda ATC 185s
81 ATC 200
Lots of other parts and bikes