1976 kz750 b1 not charging

I need to know how to hook up My reg/rec into the harness, when i test the + wire i get nothing but my stater is putting out ac voltage ????

Your bike came with separate regulator and rectifier. Are you saying you now have a combo reg/rec?

Either way, if you have adequate AC on each pair combination of the 3 yellow wires, then it would appear the rectifier is bad, or there is bad wiring on the output, input, or ground.