QuestionI have a 1970 MGB (USA built) however I'm in Australia. While driving all electric power will quit, motor dies, this fault is intermittent, the engine will most times, not always break down under load, alternator light is always on when engine is running. Could this be a short or exposed wire in the main wiring.
AnswerHi Michael. The fact that the alternator light is always on usually means that the alternator is faulty.
It is a 3-phase generator, and I guess that one of the phases has a burnt-out diode. This would allow some charging but not a lot. When you then increase the demand for power (e.g. put headlights on, turn the wipers on, or even hit the brake lights) this can be too much, and does not leave enough power for the ignition or the fuel pump.
Also, you need to get the batteries checked before replacing the alternator, because it is possible that the root cause is a bad battery. The early 1970 alternators were voltage sensing, and one bad battery can blow a good alternator. If you just fit a new alternator, a bad battery can promptly blow the new alternator.
