3-Wire Alternator Wiring Instructions

by Stephen Benham

Alternators provide an important duel function: They produce electricity to charge your battery and operate the electrical equipment in your car. Alternator wiring is easier than in the past due to the use of plugs and sockets which are usually different sizes ensuring you wire your alternator correctly. Additionally, most alternators have internal voltage regulators resulting in the need to only wire three connections instead of four.

Disconnect the two battery cables from the battery terminals before you wire your alternator. Use a wrench to loosen the clamp bolt on the end of the black cable. Lift the clamp from the battery terminal and move the cable away from the battery. Repeat the process for the red cable.

Check the back of the alternator to locate the three terminals. You may find plastic sockets, or, if the alternator is slightly older it has three metal threaded poles. One terminal is labeled "B", "Bat" or "+" while another is labeled "Gnd", "Field" or "-." The third is usually labeled "Ign", but it can vary. However the third terminal is much smaller than the other two so it's easy to recognize.

Find the three cables that connect to the alternator terminals. You will see them hanging nearby: One is a red cable, the second black, while the third is usually a striped cable and may be colored green/yellow or blue/brown. The color can vary, but you can identify the cable, as it is thinner than the other two.

Look on the end of each of the three cables to determine how they connect to the terminals. Many cables have plastic plugs that simply push in to the terminals, others have metal eyelets.

Connect the red cable to the terminal labeled "B", "Bat" or "+." If it has a plastic plug, insert the plug into the socket using your fingers as far as it can go.You will hear it click into place. Gently pull the plug using your fingers to ensure it is secure. If the cables have an eyelet on the end, then use a wrench to undo the nut on the threaded terminal pole. Place the eyelet over the pole and replace the nut. Tighten the nut using a wrench.

Connect the black cable to the terminal labeled "Gnd," "Field" or "-." If it has a plastic plug insert the plug into the socket using your fingers as far as it can go. You will hear it click into place. Gently pull the plug using your fingers to ensure it is secure. If the cables has an eyelet on the end then use a wrench to undo the nut on the threaded terminal pole. Place the eyelet over the pole and replace the nut. Tighten the nut using a wrench.

Connect the third thin cable to the last terminal. Push the plastic plug into the socket, if it connects this way. If the cable has an eyelet on the end, remove the nut from the terminal pole using a wrench and place the eyelet over the pole. Replace the nut and tighten. If you find the third terminal has a screw, then remove the screw using a suitably sized screwdriver. Place the eyelet over the screw thread, then replace the screw into the terminal and tighten using a screwdriver.

Check the three connections are secure then reconnect the two battery terminals. Place the clamp on the end of the red cable over the battery terminal labeled "Pos." Tighten the nut on the clamp using a wrench. Place the clamp on the end of the black cable over the terminal labeled "Neg." Tighten the nut on the clamp using a wrench.

Items you will need

About the Author

Stephen Benham has been writing since 1999. His current articles appear on various websites. Benham has worked as an insurance research writer for Axco Services, producing reports in many countries. He has been an underwriting member at Lloyd's of London and a director of three companies. Benham has a diploma in business studies from South Essex College, U.K.

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