Alternator Wiring

All internally regulated alternators have the same basic electrical connections. By comparing the descriptions below, it will be easy to change the instructions to suit the alternator you have chosen. If there is any doubt, take this write-up, along with the instructions for your particular car, to an alternator repair shop, and ask the counter man to identify the connections for you. Most places will be glad to oblige you, for a minimal fee, if any. Alternators typically have four external connections to the automobile's electrical system:


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Understanding Alternator Power Output

In the early days, cars used generators rather than alternators to power the vehicle's electrical system and charge the battery. That's not the case anymore. As automotive technology evolved, so did the need for more power. Generators produce direct current, which travels in one direction, as opposed to the alternating current for the electricity in our houses, which periodically reverses directions. As Tesla proved in 1887, alternating current became more attractive as it generates higher voltage more efficiently, something necessary in contemporary automobiles. But car batteries can't use AC power since they produce DC power. As a result, the alternator's power output is fed through diodes, which convert the AC power to DC power.

The rotor and the stator are the two components that generate power. As the engine rotates the alternator pulley, the rotor spins past three stationary stator windings, or wire coils, surrounding a fixed iron core that makes up the stator. This is referred to as a three-phase current. The coil windings are evenly spaced at intervals of 120 degrees around the iron shaft. The alternating magnetic field from the rotor produces a subsequent alternating current in the stator. This AC current is fed through stator leads into a connecting set of diodes. Two diodes connect to each stator lead to regulate the current. The diodes are used to essentially block and direct the current. Since batteries need DC current, the diodes become a one-way valve that will only allow current to pass in the same direction.


1. Ground. This is usually through the case, but some units require a separate connection, usually for the solid state regulator inside the case. If your unit requires a separate ground, run a short wire from the alternator to a convenient point on the engine block, or the chassis. If the connection is required for ground wire as you are using for the output, at least 10 Ga., preferably 8 Ga. 

2. Output. This connection carries the charging current from the alternator to the battery, and corresponds to the screw terminal on the back of the GM unit.  It connects directly to the battery, usually at the battery connection on the starter solenoid, or to the ammeter, if you car has one. This wire will be either Brown, or Brown with a colored stripe, in a Triumph.

3. Sensing. This wire connects to the battery, either directly, or via some connection in the main battery supply circuit. Typically, it connects to the battery side of the fuse block. Its purpose is to monitor the system voltage, and increases or decreases the charging rate, depending on the system load and/or battery condition. This is a smaller wire than used for the output, and is usually Brown or Brown with a colored stripe. This connections corresponds to terminal 2 on the GM unit. In some cases, this wire is self-contained within the alternator, and there will not be a connection for this function. If so, just omit, or insulate and tie off, the equivalent wire in the GM instructions.

4. Indicator. This lead receives voltage from the ignition switch, through the charge warning lamp, when the key is turned on, but the engine is not running. This serves two purposes - it gives a visual warning that the alternator is not charging, and provides the initial current to get the unit to charge until it can provide it's own charging current. This wire is almost always Brown/Yellow in a Triumph, and corresponds to terminal 1 on the GM unit. 

One-Wire Alternators 

Quite popular among the Street Rod set, the one-wire units are not really suited for our cars. The only advantage is the simplicity of connecting only one wire. This advantage is lost in a Triumph, because of the changes required to the existing wiring to allow the use of a one-wire unit. All the wires required for a three wire unit are in place, and would have to be disabled otherwise. There are two distinct disadvantages to the one-wire: They are more expensive, and the warning lamp function is not operable with them.

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