Check all the parts in the charging system .It might have the wrong alternator fitted to start with .And is the serpentine belt going the right way around alternator?They are not all the same directional rotation... Drop another earth strap on to the alternator bracket .And check the fuses on the top of the OVP relay if it as one fitted . Someone may have put up rated fuses in it . This little part is to stop over loads in the electrics .