The purpose of the ballast resistor is to limit current through the primary ignition circuit.
EI has a larger dwell angle than points do. This larger dwell angle leads to the current flowing in the primary circuit for more time.
This increased time results in more heating of the coil and excessive temperature in the coil will lead to coil failure. It is my understanding that the ballast resistor is there to protect the coil, not the EI module.
I have never previously read the suggestion that the igniter module has a 4 amp current limit - are you able to provide a reference?
When I first arrived on this forum I was instructed to check my coil voltage and resistance to determine whether I needed a ballast resistor. Note that it is the primary resistance you need to measure to determine whether the ballast is required.
Ndutton is the forum guru on this topic (and just a few others...)
Peter
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