How to Wire an Alternator and Starter

Use a wrench to attach the main battery cable to the starter. This cable goes from the battery to the starter and supplies full battery voltage when the starter is activated. Attach a small wire from the ignition switch to the small terminal on the starter solenoid. This controls the starter, turning it on and off when the ignition key is turned.

Bolt the starter in place with a socket wrench. This completes the wiring process. As long as the negative cable is connected to the engine block, the starter will operate. The starter completes the negative circuit through the starter case when it is bolted in place. No separate negative wire is used from the starter to the battery.

Bolt the alternator in place. Just like the starter, the negative circuit is completed through the alternator housing. Make sure that it is bolted securely to the alternator mount. Attach a cable directly from the alternator output post to the positive side of the battery. This allows for full output from the alternator to the battery when heavy electrical demands are placed on the alternator.

Wire the alternator controls. There is a plug on the alternator that has from one to three wires -- depending on the manufacturer -- that does several things. The most important connection is the power supply wire to energize the "field" connection. This powers the alternator field coils so electricity can be generated as the alternator spins. Another connection may operate the alternator warning light on the dashboard or sense the circuit voltage to operate the voltage regulator. Refer to a service manual specific to your vehicle's make and model for specific wire connections.