On my 1989 325 I put in a new alternator and battery. The car will run for a wile then die. When I test the system I only getting 12.4 volts. I cleaned all the wires. The light on the dash comes on when you start the car then will go off. When I drive I can drive for about 30 min. then the car will die. Why an I only getting 12.4 volts out put from the alternator?