blowing tail light fuse/ charging problems

Ok so here's the problem. I have a 1977 b2 kz750 twin and mechanically it runs like a champ. but as for electrics its always had a gremlin. its had a charging problem from day one and so i have replaced the stator the roter and the coil feild and i got a brand new regulator rectifier from oregonmotorcycleparts.com and now it still wont charge.

Go to www.electrosport.com and find their troubleshooting page, it's got good tips on how to check the charging output.