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Electrical Instructions for Replacing the Alternator with a GM Alternator in a TR6

by Dan Masters,

Method One (Utilizing existing wiring)

At the stock alternator, you will find either a five, or a three, wire connector. If you have the five wire connector, you will find a large Brown/White wire, a smaller Brown/Red wire (except for '73, which uses a Brown wire), and what appears to be three Brown/Yellow wires.

What appears to be three Brown/Yellow wires are actually only two. At one terminal, you will find two Brown/Yellow wires, and at another, you will find one. The single Brown/Yellow wire actually goes into the harness for a very short distance, and then turns around and comes back out, where it connects to the terminal with another Brown/Yellow wire. If you pull on the single Brown/Yellow wire, it will pull out of the harness, and you will see what I mean. You may have to loosen the harness a little bit to get it to pull out. That short piece of Brown/Yellow wire is to be discarded.

If you have a three wire connector, the short piece of Brown/Yellow wire has already been removed - either by the factory, on '74 and later models, or by a previous owner when he replaced the alternator with a later model. For '69 - '73, with an owner modification, the wire colors will be as above. For '74 and later, there will be a large Brown wire, a smaller Brown wire, and a small Brown/Yellow wire.

The large Brown/White (Brown) wire is the main charging lead. The small Brown/Red (Brown) wire measures the system voltage to tell the alternator how much to charge. The Brown/Yellow wire(s) operates the alternator warning light, and provides the initial voltage to the alternator to start it charging when the engine first starts.

Of course, Disconnect the ground lead from the battery before proceeding with any electrical work, and follow all the rules of proper wiring practices. I recomend using solder connections, and covering them with heat shrink tubing, but crimp type connectors will work quite well also. You will need butt connectors for attaching to the plug wires, and a large ring connector for the screw terminal. If you would prefer not to have splices, you can remove the terminals, and the wire, from the plug. Using new terminals of the proper type, connect directly to the existing wires, and insert the terminals into the plug. New terminals can be purchased from British Wiring, (20449 Ithaca, Olympia Fields, IL 60461, 708-481-9050) and The Wire Works (167 Keystone Road, Chester, PA 19013, 800-292-1940), among others. . Regardless of whether you have an early model TR6 with the ammeter, or a later model with the voltmeter, the meters will now work just as before, as will the alternator charge warning light.

There are two things, however, to be aware of:

  1. Triumph did funny things when they built these cars, so your car might not match the configuration above, and it may well have been modified by a previous owner.
  2. The factory alternator output ranged from 28 amps on the early cars, to 45 amps on the later cars. The GM units can produce 55 or more amps. The wiring in the cars is only designed for the lower rating of the stock alternator. If you add heavy loads, driving lights, high power stereo, etc, you can exceed the capacity of the wires. Also, If you let the battery discharge completely, the alternator can possibly recharge with enough current to overload the wires. If your battery is completely discharged, recharge it with a charger rather than push starting the car and letting the alternator recharge it. If you must do this, keep a close watch on the ammeter, checking for overcharging. Under all other usages, the wiring should not present a problem. The main advantage of the higher output is the ability to provide a higher charge rate at low RPM and idle. The standard loads on the TR6 do not require a higher charge current at normal engine speeds, so the alternator will not be called on to provide enough current to overload the wires.

Method Two (Upgraded wiring)

If you wish to upgrade the wiring to take advantage of the higher output, it is really quite simple.

As above, except:


There are several other ways to do the replacement. For example, you may wish to use a larger range ammeter, or you may wish to replace the ammeter with a voltmeter. If so, contact me with your preferences, and I will try to provide the appropriate instructions.

You may also choose to use a different alternator , rather than the GM unit. If so, it will be wired very similarly to the above, only the connections at the alternator itself will be different.


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