The MGA With An Attitude

This is your basic guide to MGA wiring color codes and trouble-shooting. Most electrical problems can be easily diagnosed in a few basic steps: Identify the problem, refer to the wiring diagrams, trace through the circuit connector by connector starting at one end (usually the hot side) until the problem is found. In general, wire end connectors may be loose or corroded, but the wires will usually be okay. All of the wire connections are outside of the wiring loom, so there is no reason to cut into the harness binding.

The single most essential tool for electrical trouble-shooting is a test light. This can help you diagnose about 90% of all problems you may encounter, and can be purchased for a few dollars. Without a test light, all you can do is wiggle some connectors and cross your fingers. The next tool that is occasionally handy and helpful with some tougher problems is a Volt-and-Ohm meter, commonly known as a VOM. Some small analog VOMs can be purchased for as little as $10, while a nice pocket size digital unit (DVM) can be had for less than $30.

Following is a short list of the basic color codes used for the primary circuits. If you can remember these eight primary colors and what they mean, you're well on your way to understanding Lucas electrics.

BROWN = Battery Circuit. Originates at control box terminals A and A1, feeds the ignition switch and lighting circuits unfused, and also the horn through a fuse. Brown wires are ALWAYS HOT. Accessories can be installed at fuse box terminal A1, but should always be fused separately.

YELLOW = Generator Circuit. Generator terminal D (armature, a.k.a. dynamo) to control box terminal D and ignition warning light. These wires will be hot with IGNITION ON.

WHITE = Ignition Circuit. These wires feed circuits that are hot with the IGNITION ON, and are NOT FUSED.

GREEN = Auxiliary Circuits. These wires are fed from the ignition switch, are hot with IGNITION ON and are FUSED.

BLUE = Headlamp Circuit. These circuits are fed from a terminal on the light switch and are NOT FUSED.

RED = Side and Tail Lamp Circuits. These circuits are fed from the S1 or T terminals on the light switch, including fog lamps and panel lamps, and are also NOT FUSED.

BLACK = Grounded Circuits (Earth connections). Any components not internally grounded are grounded to the chassis. These wires are not fused, but should always show 0 volts and 0 ohms in relation to the earth terminal of the battery. If you have dim bulbs or slow flashers, think "bad ground". Any black wire which shows voltage or lights a test lamp has a bad chassis connection.

One additional general note on color codes. Once a circuit passes a switch it will have a secondary color stripe. A ground return circuit passing through a switch will generally be black with a white stripe.

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