Actually the current that the ignition system uses is minimal as far as
overloading the charging system is concerned. The charging system could
care less about how much the ignition is drawing unless of course a dead
short were to develop but at that point the engine would stop anyway. The
charging system , even at a low 35 amp rating for alternator equipped cars
( no AC for example ) has far and above the capacity to keep up with
ignition demand. The charging system will do whatever it can to keep a
nominal 14 volts supplied, which is why it puts out more current as the
demand increases, to try and keep the voltage at the desired value.
As far as ignition system current goes, 3 amps is more like nominal for
older points style equipped vehicles. In fact, the 62 FSM shows an ignition
system amperage draw from 1.9 to 3 amps depending on engine speed. It is a
given that at higher speeds there is less time available for the coil to
saturate which is the reason the transistorized ignition came into use, a
transistor is infinitely faster than a set of points in that respect and the
problem of point burning and dwell change with rpm is no longer a problem.
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