The process for wiring a starter and an alternator on a car is divided into two parts. The first part deals with the power circuit connections because starters consume and alternators produce great amounts of power. The second part involves the control circuits. Starters are turned on and off, and alternator output is regulated, both by their respective control circuitry. By breaking the wiring process down into two categories, the job is easier to understand, and the results are much more predictable.
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 energise 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.