How to Wire a 3 Wire Alternator

Written by k.k. lowell
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With the trend to 1-wire alternator use for hot rods and other vehicles, the 3-wire alternator has lost some popularity. This is too bad, as the 3-wire is a more economical, readily available choice. This alternator is also a wiser alternative for those vehicles where the battery is not mounted close to the alternator, as it can sense the voltage at a remote point and keep a distant battery more fully charged. Wiring a 3-wire alternator is not, obviously, as simple as wiring a 1-wire, but it is not difficult and doesn't require any special tools.

Skill level:
Moderately Easy

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Things you need

  • 10-gauge automotive wire
  • 14-gauge automotive wire
  • Replacement alternator connecting plug
  • Soldering gun
  • Solder
  • Terminals
  • Heat shrink tubing

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  1. 1

    Disconnect the vehicle battery.

  2. 2

    Insert the replacement alternator plug into the receptacle on the rear side of the alternator.

  3. 3

    Cut a short piece of heat shrink tubing and slide it on the pigtail from terminal number 1 on the new alternator plug.

  4. 4

    Connect a 14-gauge wire to the pigtail and solder in place. Cover with the heat shrink tubing, which can now be heated and shrunk to insulate the connection. Connect the other end of the 14-gauge wire to the IGN or ACC terminal of the ignition switch.

  5. 5

    Splice a 10-gauge wire to the number 2 pigtail on the alternator plug and insulate with heat shrink tubing. The other end of this wire can be connected to the same place on the starter solenoid as the battery positive cable, or, in the case of a remotely mounted battery, to the positive terminal at the battery. This wire is the voltage-sensing wire, so connection at or near the battery is best.

  6. 6

    Cut another length of 10-gauge wire and connect to the voltage output stud on the back of the alternator and the starter solenoid. Connect to the same stud on the solenoid as the battery positive cable.

  7. 7

    Reconnect the vehicle battery.

Tips and warnings

  • A light can be wired in series in the 14-gauge wire to indicate if the alternator should fail.

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