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Bill Sinclair was the feature speaker at this meeting and gave a very informative talk about the infamous Lucas wiring system. As he said, it’s not that difficult, once you understand what each coloured circuit is doing. Here is a summary of what Bill had to say. I hope I got it right!!!

British sports cars have a very simple and effective wiring system, and it’s pretty easy to understand once broken down into circuits. Some of the reputation for difficulty dates back to the older cloth-braided wiring, which would fade with age to a uniform colour. This made tracing the wiring an interesting guessing game. More modern vinyl wiring is much easier to trace and identify. The colour rules are the same for most British cars. The main wire colour identifies the type of circuit.

Brown – Battery Circuit; Live all the time. Unfused, so be careful what you touch. These are the wires that go to the alternator and feed the fusebox, ignition and lighting switches.

Purple – Unswitched Auxiliary Circuit: This circuit is fused and provides power to items such as the lighter socket, trunk, and interior lights. (all of which remain powered when the ignition is switched off).

White – Ignition Circuit: Switched by the ignition switch, unfused, so again make sure that these wires do not get cut. From the ignition switch this circuit powers the electric fuel pump if fitted, coil, and provides an ignition switched feed to the fuse box to power the auxiliary circuit.

Green – Switched Auxilary Circuit: Switched by the ignition switch, this circuit is fused and powers the turn indicator, stop lamps, gauges and windscreen wiper/washer.

Red – Side and Tail lamp Circuits: Switched by the headlight switch, this circuit also feeds the dash illumination lamps through either a switch or rheostat.

Blue – Headlamp Circuits: switched by the headlight switch, this circuit feeds the high/low beam switch, which in turn feeds the headlamps.

Black – Earth (Ground) Circuits: These wires provide the return path down the chassis. Many problems can be traced to poor chassis connections due to corrosion or new paint.

Knowing these basic circuits, and armed with a test light, many common problems can easily be traced. Problems usually involve poor continuity at switches, connectors, or the fuse box.

The Secrets of the LUCAS Electrical System Revealed

All electrical components and wiring harnesses depend on proper circuit functioning, which is the transmission of charged ions by retention of the visible specral manifestation known as "smoke". Smoke is the thing that makes electrical circuits work. Don't be fooled by scientists, engineers or mechanics talking about excited electrons, the valance layer of the copper molecule and the like. Smoke is the key to all things electrical.

We know this to be true because every time one lets the smoke out of an electrical circuit, it stops working. This can be verified repeatedly through empirical testing. For example, if one places a large spanner across the terminals of a battery, prodigious quantities of smoke are liberated and the battery shortly ceases to function. In addition, if one observes smoke escaping from an electrical component such as a voltage regulator, it will also be observed that the component no longer functions.

The logic is elementary and inescapable! The function of the wiring harness is to conduct the smoke from one device to another. When the wiring harness springs a leak and lets all the smoke out of the system, nothing works right afterward.

Sometimes you may miss the component releasing the smoke that makes your electrical system function correctly, but if you sniff around you can often find the faulty component by the undeniable and telltale smoke smell. Often this is a better indicator than standard electrical tests performed with a volt-ohm meter.

In conclusion, the basic concept of transmission of electrical energy in the form of smoke provides a clear and logical explanation of the mysteries of Lucas electrical components and why they fail.

I learned a long time ago that once you let the "Factory Smoke" out of any electrical device, it is next to impossible to replenish it.


Copyright 2006
Okanagan British Car Club