M/P Voltage Regulator Yes or No?

i had a powermaster 75 amp use to charge at about 14 volts running 2 fans and an electric fuel pump . it was fine until the neutal switch wire burned on the header and shorted out . i cant get the thing to charge over 13.2 then the regulator over heats and fails . of coarse some one changed the wiring at the fuse block and i dont no what the hell is what perhaps a new extenal wiring harness would help me. you guys are a wealth of information.