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 FR signal - The 
transistor activation signal inside the alternator monitors the voltage 
generated by the alternator to control the excitation current before it 
sends the FR signal to the ECM. (At certain RPM/electric loads, the FR 
duty can remain static. However, more often, the RPM, electric load, 
target voltage, etc. are always changing in the vehicle, so the FR must 
also change constantly)  |