1959 D 14 that has been wired for 12v negative ground. It has a 12v Delco generator and new 12v Regitar regulator. It is not charging only reads 12.4 v across battery when running at any RPM. Lights, starter,everything works fine. I have polarized regulator by jumping 12v to field, I get the small spark. I have read to test generator to apply 12v to generator field post and some say to ground the generator field. I have applied 12 v and charging voltage does not change. I have disassembled generator and cleaned. The field windings check good and brushes look good. Any ideas? Thanks