How to Wire an OBD2 Alternator on an OBD1 Engine / Chassis First step, cut off the OBD2 alternator plug from any unused OBD2 engine harness. Second step, cut off your OBD1 engine harnesses alternator plug. Third step, match color for color below the four alternator wires and solder/ heatshrink each for a trouble free connection: black with yellow stripe = black with yellow stripe.[PDF] Understanding the Alternator - Autoshop 101 Understanding the Alternator • 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.