Triumph Alternator Conversions

by Dan Masters,

This article provides an introduction to alternator conversions, as well instructions for a number of various conversions, and owner experiences. If you would like to add your experiences to these pages, send mail to the webmaster .

Quick Index:

Problems with Original Equipment

There are three problems with the Lucas generators and alternators that came with our Triumphs:

  1. They are weak, especially at idle.
  2. They are expensive to replace.
  3. They are very rarely available locally.


Fortunately, it is not very difficult to replace your alternator with one that is cheap, readily available, and with a much higher output. What alternator to use? Actually, it doesn’t make any difference – any alternator that can be made to fit physically will do. Your choice will depend on the relative configuration of your engine and the alternator you select. What might be just perfect for one application may not work without extensive modification on another, and vice-versa. The only overriding criteria should be that the alternator you choose should have an internal regulator. Externally regulated alternators work just as well, but there is an added complication with them, with no offsetting advantage.

One of the best choices is the GM alternator – it is cheap (less than $30), available off the shelf at nearly any auto parts store in the country, and can be had with an output of 55 or more amps, up to 100 if you want to pay more! It can be had with the electrical connections at any one of four possible locations – top, bottom, right side, or left side (refered to as the “clock,” 12, 3, 6, or 9 O’clock) – which can be of great help when rewiring your car to use the new alternator. Just tell the counter man where you’d like the connections to be, and he most likely can find one in stock to match.

Regardless of which brand you choose, the physical mounting problems are usually not too hard to overcome by most backyard mechanics; it’s the electrical connections that give the trouble. Using the instructions referenced at the end of this section, anyone should be able to swap their anemic Lucas generator or alternator with a modern, more powerful, and more easily obtained unit. Because I am familiar with the GM alternator, I have provided detailed instructions for converting the generator or alternator in various Triumphs to this unit. If you wish to use another make, however, the following equivalencies should aid in modifying the GM instructions to apply to your unit.

Alternator Wiring Connections

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:

  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 the regulator, a small wire, 14 Ga., is adequate. If it’s for the alternator itself, use the same size 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. It’s 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.

Model Specific Electrical Instructions for Conversions

Actual Experiences from Reader Submissions


The above article has been provided courtesy of Dan Masters,

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