COM signal - When controlling the generated voltage, the ECM sends target voltage data to the alternator via a PWM signal. (High voltage: 4 V or higher; low voltage: 2 V or lower)
FR signal - The transistor activation signal inside the alternator controls the alternator output voltage to regulate the field current, before it sends the FR signal to the ECM. (At certain engine speeds/electrical loads the FR duty may remain unchanged. However, in most cases engine speed, electrical load, target voltage, etc. change constantly in the vehicle, so the FR duty must also change constantly.)
L signal - The battery warning lamp on the instrument panel illuminates when the charging system malfunctions. (Lamp illumination conditions - overcharge, overdischarge, field coil burnt out inside the alternator.)
B+ terminal - The output voltage from the alternator is supplied to the battery through the B+ terminal.
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Test yourself
A quick Hyundai Tucson LM quiz: every answer comes with an explanation and a link to the manual page.
