Circuit Diagram

Fig 1: ECM & Alternator Circuit Diagram

Courtesy of HYUNDAI MOTOR AMERICA

Information 

• COM signal 
  • When controlling the voltage generated, the ECM sends the target voltage data to the alternator via a PWM signal. (High voltage: 4V or higher, low voltage: 2V or lower)
• 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)

• L signal - 

  Turns on the battery warning lamp on the dashboard when the battery charging system malfunctions. (Conditions for turning on the lamp - overcharge, over discharge, a field coil blown inside the alternator)

• B+ terminal-  The output voltage from the generator travels to the battery via the B+ terminal.