Understanding the Alternator

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The Charging System Circuit

Four wires connect the alternator to the rest of the charging system.
'B' is the alternator output wire that supplies current to the battery.
'IG' is the ignition input that turns on the alternator/regulator assembly.
'S' is used by the regulator to monitor charging voltage at the battery.
'L' is the wire the regulator uses to ground the charge warning lamp.