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▷▷ 2021 ▷ How to connect an alternator and a starter motor

6 julio, 2021

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by Jack Hathcoat

custom image car1 by Bhupesh Shah from

The process of wiring a starter and alternator in a car is divided into two parts. The first part deals with the power circuit connections because starters draw and alternators produce large amounts of power. The second part involves the control circuits. The starters turn on and off, and the alternator output is regulated, both by their respective control circuits. By dividing the wiring process into two categories, the job is easier to understand and the results are much more predictable.

Step 1

Use a wrench to connect the main battery cable to the starter motor. This cable runs from the battery to the starter motor and supplies full battery voltage when the starter motor is activated. Connect a small wire from the ignition switch to the small terminal on the starter solenoid. This controls the starter motor, turns it on and off when the ignition key is turned.

Step 2

Screw 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 run. The starter completes the negative circuit through the starter case when bolted into place. No separate negative cable is used from the starter motor to the battery.

Step 3

Screw the alternator in place. Like the starter, the negative circuit is completed through the alternator housing. Make sure it is screwed securely to the alternator bracket. Connect a wire directly from the alternator output post to the positive side of the battery. This allows full output from the alternator to the battery when high electrical demands are placed on the alternator.

Wire the alternator controls. There is a plug on the alternator that has one to three wires, depending on the manufacturer, that does several things. The most important connection is the power cord to power the “field” connection. This powers the alternator field coils so that electricity can be generated as the alternator rotates. Another connection can operate the alternator warning light on the dash or detect the circuit voltage to operate the voltage regulator. Consult a specific service manual for your vehicle make and model for specific wire connections.

Articles will need

  • 3/8 inch socket set
  • Keyset

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