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Electrical Instructions for Replacing the Alternator with a GM Alternator in a Spitfire MKIV, Spitfire 1500, GT6 MKII or a GT6 MKII

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 wire, a smaller 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 or by a previous owner when he replaced the alternator with a later model.

The large Brown wire is the main charging lead. The smaller 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.


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